Page images

papillæ upon which they are seated. In some worms bearing a close relationship to this species the papillæ are so large as to affect the two adjoining segments (14-16), but, in this case, no such prominent position is held by them. The girdle is conspicuous, dense, and closely fused on the dorsal surface, but each segment is clearly defined beneath. It covers six to eight segments, two only of which bear the tubercula pubertatis. The general outline of the girdle ventrally closely resembles that of the nearly allied mucous worm (A. mucosa, Eisen), as it is truthfully pourtrayed by Eisen in the plate which accompanies his original description. We shall the better understand this after studying the details supplied in the next section.

One rather striking peculiarity may here be emphasized. In several species of worms, such as the brandling (A. fætida, Sav.), the long worm (A. longa, Ude), and the common earthworm (Lumbricus terrestris, L.), we find a tendency on the part of those segments which contain the sexual organs to become tumid and pale on the ventral side. In this case, however, it is the dorsal surface which is so affected, especially in segments 10 and 11, and on the worm being dissected the cause of this unusual appearance is at once discovered. Whereas in most species of worms the spermathecæ are ventrally or laterally placed, in the Irish worm they are disposed on the back.

II.-SYSTEMATIC Account of SPECIMENS. I was fortunate enough to find eight specimens of this worm in the batch consigned to me, and had recognised the novelty of the worm as soon as the first specimen or two had been transferred to alcohol, so that I was able deliberately to study the whole series, first in a living state, and afterwards in spirits. I have since received two large series of the same worm from Dr. Scharff, by means of which I have been able to confirm and extend my earliest observations. As the characters by which the species is distinguished in a living condition have now been generally set forth, I will proceed to specify some details respecting the individual specimens as they appear when preserved in alcohol. Not one of the specimens carried spermatophores, but six out of the eight were sexually mature, and the other two were in a specially good condition for external diagnosis. One of the most important points in relation to the classification of worms is that which concerns the number and position of the tubercula pubertatis and it frequently happens that the exact solution of the difficulty is accomplished with the greatest ease when the worms are in a state of puberty. Earlier in life there is absolutely nothing to differentiate one segment from

another, while the fully developed girdle of later life sometimes obscures these organs, as for example very notably in the turgid worm (A. turgida, Eisen). There was not the least difficulty in the present instance, owing to the fact that the two immature worms had reached the period of pubescence, and showed the glandular prominences known (fig. 6.) as the tubercula pubertatis most distinctly on segments 30 and 31. There are, therefore, a pair on each side, and as the segments bearing them thicken, and develope the girdle, this portion of the body attains the greatest diameter.

A bird's-eye view of the whole will be best obtained by means of a chart in which the points of importance may be tabulated in detai). The measurements were all made after the animals had been placed in alcohol.


[merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][ocr errors][ocr errors][merged small][merged small][ocr errors][ocr errors][ocr errors][ocr errors]

It will be seen that the number of segments ranges between 86 and 108, so that the average is about 100. The length when contracted does not exceed 15 inch or 34 mm., while the youngest specimen falls just short of an inch. The range is more limited than in some of the larger species, and there is much greater uniformity in other particulars as well. There was not the least trace of an exception with regard to the tubercula, and with reference to the girdle the divergences are very small. Three specimens had seven (figs. 5, 6) segments (27—33) involved, and three had six (27-32 or 28–33), showing what I believe to be a tendency towards reducing the girdle to the limits reached by the genus Lumbricus.

While the worms are perfectly cylindrical in alcohol, with the tail rapidly coming to a point, as in the green worm (A. chlorotica, Sav.), yet, when in motion, the hinder part frequently appears flattened and somewhat spatulate. The anal segment is large, while the first ten or dozen segments are about double the diameter of the rest, with the exception of the segments which form the girdle in the mature worm. The setae are disposed somewhat as in the gilt-tail (A. subrubicunda, Eisen), but are not placed on pale gland-like sacs as they usually are in the finest forms of that species. In the gilt-tail also the segment behind that which carries the male pores is tumid ventrally, frequently forming a conspicuous ridge along the under-surface of the body, whereas no such tumidity is seen in any of the specimens of the Irish worm submitted to me. On one of the specimens (No. 7) there were glandular prominences or papillæ developing under the 24th segment. Such papillæ are a striking feature in many earth-worms, and are concerned with the sexual relationships of the animals carrying them. It may be observed also with reference to another specimen (No. 5) that though it has the smallest number of segments, it is exactly midway between the two extremes in point of length. Having studied some hundreds of abnormal worms, I find that whenever the number of segments in an adult worm falls below the average there is a tendency for the segments to increase their longitudinal diameter. This inclines one to the opinion that there is a normal length which it is desirable for each worm to attain if it is to discharge the functions of life in the fullest and best possible manner.

Important as external characters are, and readily as the great bulk of worms may be assigned to their true genus and species without the least study of internal organs, it is nevertheless of the utmost importance that the sexual organs of each species should be carefully examined, and their number and position defined. Rosa, the eminent Italian biologist, has clearly pointed out on more than one occasion how necessary it is, not merely to examine the spermathecæ, but especially to notice the position of the opening by which their contents are capable of being passed from within outwards. We shall have in the next section to reiterate this fact; for the present, then, we will be content to examine the species in hand.

Opening a specimen of the Irish worm by a latero-dorsal incision extending from the girdle tothe lip, we are able to display every organ

are exposed 10:11. Two pairs ve the reason for the es, spermathecæ,

of the body-intestine, gizzard, nephridia, seminal vesicles, spermathecæ, &c. (fig. 9.) Instantly we perceive the reason for the dorsal tumidity

pr. are exposed to view, lying in the 9th and 10th segments. The posterior pair is about twice the size of the anterior, and thus tends to fill up the segment immediately behind that in which it properly lies.? A cord or duct connects each of these 5m important bodies with the integument, and they are clearly seen to open into the median-dorsal line near to the place usually occupied by the dorsal pores. They are attached to the anterior face of the septum, and thus connect themselves with the 9/10th and 10/11th intersegment. This is the crucial point so far as internal anatomy is concerned ; and while much might be written 10 sm about the other organs, the neglect of this point might result in very erroneous conclusions.

[ocr errors]

Fig. 9. III. AFFINITIES. The specimens under examination were found associated with three species of Lumbricus, together with the green worm, brandling, and gilt-tail. It was evident at first sight that its direct affinities were not very strongly with either of these species. Michaelsen, however, described a form two years ago which seemed at once referable to that under discussion. In an article on Die Lumbriciden Norddeutschlands (Jahrb. der Hamburg. wiss. Anstalten, vii.) he speaks of a worm which was supposed to be a variety of the gilt-tail, but differed from the type (A. subrubicunda, Eisen) in having the tubercula pubertatis on segments 30 and 31, instead of on segments 28, 29, 30. Besides this there was a difference in the disposition of the setæ. Michaelsen, however, failed to examine the structural details of the worm's internal anatomy, or he would have found at once, what the external facts indeed pretty clearly indicated, that the two worms were not in the least intimately related.

It remained for Dr. Rosa to assign to the worm described by Michaelsen as “ Allolobophora subrubicunda, Eisen, forma nov. hortensis" its true position. In the “ Atti del R. Inst. Venet.' iv. (1885–6), p. 674, Rosa gives an account of the earth-worms of Venice, and

1 This difference in size is not a permanent character, but depends on the maturity of the organs.

among others makes mention of a new species, which he designated the Venice worm (A. veneta, Rosa). As this worm corresponds in some particulars exactly with the Irish worm (A. hibernica, Fr.) I think it necessary to transcribe the principal portion of Rosa's description, taken both from his original memoir, and from the synopsis of the same published in the Boll. Mus. Zoolog. Anat. Comp. Torino," vol. i., No. 3 (Ap. 15, 1886).

DESCRIPTION OF A. veneta, Rosa. Length in alcohol from 50 to 70 mm., or an average of 60 mm.; diameter immediately behind the girdle, 5 mm. Segments averaging 140, or ranging from 120 to 150. In form and colour exactly like the brandling (A. fætida, Sav.). Cylindrical in alcohol, but with the hinder part polyhedric, owing to the disposition of the setæ. Very large from the head up to the girdle, then rapidly attenuated towards the anal extremity. Segments occupied dorsally by a band of reddish pigment, with other points of resemblance to the brandling. Prostomium pale, the prolongation occupying one-third of the first segment or peristomium. Instead of the pallid spot found on the brandling under segments 9:10:11, one here usually finds a white aureole on segment 12 at the base of the 3rd and 4th setæ. The male pore is as usual on segment 15, with very small papillæ, the setæ near the apertures being affected. The girdle occupies segments 27.–33 ( = 7), rarely 27-32 (= 6), or 26–33 (= 8). The tubercula are in two pairs on segments 30 : 31, and are well seen in young examples, in which the girdle is not yet developed. Setæ in pairs, but not closely approximated. The spermathecæ are disposed exactly as in the brandling, viz. a pair in segment 9, and another in the 10th segment against the posterior dissepiment, and opening into the intersegments 9/10, 10/11 in the neighbourhood of the mid-dorsal line. The seminal vesicles also correspond with those of the brandling. The worms are very active, and emit abundance of yellow fluid from the dorsal pores. At first sight, and especially in the matter of colour, it is impossible to distinguish this species from the brandling, although the wide pairing of the setæ rather suggests association with the Alpine worm (A. alpina, Rosa). The tubercula, however, serve at once to distinguish these three species.

In 1889 Dr. Rosa published a note on a worm found in the Botanical Gardens of Coimbra, in Portugal, as well as in Liguria, the characters of which showed it to be a variety of the foregoing. From what we learn respecting it we may judge that it approaches the form described

« PreviousContinue »