DRS. CARPENTER AND CLAPAREDE ON TOMOPTERIS OMSCIFORMIS. 05 
specimen, represented in fig. 14, was not more than -A-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 noticeable features of difference from the more 
advanced form : — The " frontal horns " were entirely wanting. The first antenna' (a, a) 
were relatively very long, but presented only a trace of articulation. The second antenna- 
(b, b) were relatively very short, and presented a bifid termination which clearly indicated 
their homology with the ordinary members ; only one of the pinnulae 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 pinnulae only, which were sessile 
on the trunk of the body, the lateral extensions which bear the pinnulae 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 pinnuhc, however, in the two 
most developed pairs of appendages, a single sulphur-yellow "roset ten fornixes Organ" 
presented itself. The ventral surface of the pinnulae, 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 Tomoptcris of tolerably advanced 
development (the caudal prolongation beginning to show itself) we found the pinnula- 
covered with large trichocysts 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 usually seen in Para- 
mecium aurelia, P. bursaria, and other Infusoria, having been frequently observed by us to 
be wanting in those of particular collections of water. 
i 
It will, we think, be obvious from the details w r e have given of the structure of this 
interesting creature, that it is a degraded form of the Annelida* type, — its nearest affini- 
ties being (as already pointed out by Drs. Leuckart and Pagenstecher) to the chaetopod 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 liigher 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 represents 
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 un 
<>■ 
* See Prof. Huxley's Lectures in * Medical Times and Gazette,' July 12 & 26, 1856. 
VOL. XXIII. 
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