356 DR. W. B. CARPENTER ON TOMOPTERIS ONISCIFORMIS. 



ing to the styliform appendage ; and the membranous sheath of its stylet was studded at 

 intervals with isolated red granules or minute cells, which appeared to me to be connected 

 by delicate fibres having the same general resemblance to the axis-band of ordinary nerve- 

 fibres. I do not speak with any confidence on this point ; more especially on account of 

 the a priori improbability of the longitudinal nerve-cord being on the doi'sal aspect of the 

 body. But I think it right to record the fact of the constant presence of these red spots 

 (of which very little notice has been previously taken), and of the apparent existence of 

 fibres passing between them. 



The impression at first left on my mind by the study of this interesting creatui-e, of 

 which I had never before seen or heard any account, was that it was a larval form, per- 

 haps of an Annelid, but not impossibly of some Isopod Crustacean ; the latter notion 

 being suggested by its strong resemblance in habit to the Branchiopod forms of that 

 class. I tried every expedient I could think of, for preserving specimens for subsequent 

 examination and exhibition; but I could not succeed. Any medium in the slightest 

 deo-ree different in density from sea-water caused either an immediate endosmose, by 

 which the body was made to burst, generally at the ends of the members ; or an exosmose, 

 by which it was at once shrivelled-up ; and the tendency to disintegration which I have 

 already noticed as showing itself even during life, operated still more strongly so soon as 

 life became extinct. 



Not many days after I had made the observations already detailed, I captured a speci- 

 men of larger size, having Iwelve pairs of fin-like appendages, and a caudal prolongation 

 destitute of appendages, — its structure being in every other respect the same. And after 

 a few days more I was fortunate enough to obtain (along with several specimens of the 

 younger form) the specimen represented in fig. 6, which can scarcely be considered as 

 anything else than another phase of the same type. Its entire length was about 2| times 

 as great ; but of tliis only about the anterior three-fifths corresponded in structure to the 

 original, the posterior two-fifths being obviously an addition formed upon a very different 

 plan. Looking first to the anterior portion, we observe that it differs from fig. 1 in the 

 following particulars. The head appears to carry on its front only one pair of horn-like 

 appendages; a careful examination, however, shows that the second or smaller pair is 

 really present, though, from its arising from the under side of the peduncle (which is 

 here relatively shorter), it is concealed by the anterior part of the head when viewed from 

 the dorsal aspect. The styliform appendages are greatly increased in relative length, so as 

 even to pass considerably beyond the anterior three-fifths of the body. 



The number of fin-bearing appendages is now sixteen ; of these the first eight are nearly 

 of equal size ; and there is then a gradual diminution down to the 16th, which, though 

 comparatively smaU, presents the structure characteristic of the rest. The alimentary 

 canal, instead of being limited to a portion of the cavity of the body, now fills it entirely, 

 except in the pharyngeal region ; and it seems to be in a state of constant distension, 

 except where narrowed at any part by a wave of peristaltic contraction which occasion- 

 ally passes from the mouth to the anus. Such a narrowing is seen between the 12th and 

 13th pairs of fin-like appendages, and is shown on a larger scale at the top of fig. 7. The 

 structure of the canal remains quite simple as far as the 16th pair of appendages, and 



