DRS. CARPENTER AND CLAPAREDE ON TOMOPTERIS ONISCIFORMIS. 65 



specimen, represented in fig. 14, was not more than ^5-th of an inch in length, and 

 seems to correspond in its grade of development with one which came under the observa- 

 tion of Busch. The following are its most noticeahla features of difference from the more 

 advanced form : — The " frontal horns " were entirely wanting. The first antennsB {a, a) 

 were relatively very long, but presented only a trace of articulation. The second antennae 

 (5, b) were relatively very short, and presented a bifid termination which clearly indicated 

 their homology with the ordinary members ; only one of the pinnulse was setigerous, and 

 it would seem as if this alone were destined to undergo further development, while the 

 other becomes obsolete. Behind these were only four pairs of lateral appendages, the 

 fourth being as yet rudimentary ; these were formed by pinnulse only, which were sessile 

 on the trunk of the body, the lateral extensions which bear the pinnulse at a later period 

 not having been as yet developed. No trace was to be seen either of the ciliated canals 

 or of their rosette-like orifices ; near the junction of the pinnulse, however, in the two 

 most developed pairs of appendages, a single sulphur-yellow " rosettenformiges Organ " 

 presented itself. The ventral surface of the pinnulse, and the surface of the whole poste- 

 rior part of the body, were ciliated. The body was bifurcated at its posterior extremity. 



We think it proper to record the fact, that in a single Tomo])teris of tolerably advanced 

 development (the caudal prolongation beginning to show itself) we found the pinnulee 

 covered with large irichocysts or thread-cells (fig. 11). Notwithstanding a careful search, 

 we failed to meet with these in any other individual. However strange this circumstance 

 may appear, it is not altogether without parallel, — the trichocysts usiially seen in Fara- 

 mecium aurelia, P. bursaria, and other Infusoria, having been frequently observed by us to 

 be wanting in those of particular collections of water. 



It will, we thinkj be obvious from the details we have given of the structiire of this 

 interesting creature, that it is a degraded form of the Annelidan type, — its nearest afiini- 

 ties being (as already pointed out by Drs. Leuckart and Pagenstecher) to the chsetopod or 

 setigerous Annelids. Every part of the characteristic organization of that type is here 

 reduced to the extreme of simplicity. The alimentary canal passes in a straight line from 

 one extremity of the body to the other, without either sacculations or glandular append- 

 ages. The nutritive fluid which transudes through its walls, and. which thus finds its way into 

 the perivisceral cavity, is distributed throughout the body solely by means of extensions of 

 that cavity ; through which it is propelled in part by the agency of the cilia that clothe 

 its walls, and in part by the general movements of the body and appendages. This fluid 

 is so obviously the homologue of the blood of higher animals, that we cannot but regard 

 the existence of the type of structure before us (the wonderful transparency of the body not 

 permitting the slightest doubt as to the absence of anything resembling a dorsal vessel) as 

 affording a further confirmation of that view of the (so-called) circulating apparatus of the 

 higher Annelida, which regards their perivisceral cavity and its extensions as representing 

 the proper sanguiferous system, and which looks upon the system of vessels containing 

 coloured fluid as a special arrangement having reference rather to the respiratory func- 

 tion*. The extreme tenuity of the walls of the body and of its appendages, renders it uu- 



* See Prof. Huxley's Lectures in 'Medical Times and Gazette,' July 12 & 26, 1856. 

 VOL. XXIII. Iv 



