62 DRS. CARPENTER AND CLAPAREDE ON TOMOPTERIS ONISCIFORMIS. 



and the alimentary canal is thrown by this contraction into convolutions, which are 

 sometimes slight and easily distinguishable, as shown in Plate VII. fig. 2, but which, 

 when the caudal appendage is greatly contracted (as shown in figs. 6 & 7 of Plate LXII. 

 vol. xxii.), may be so close as to render it difficult to follow their course, by reason of the 

 opacity which the part then acquires. The part of the intestine contained in the caudal 

 prolongation has its external surface clothed with cilia; but these are most apparent 

 along particular bands. Cilia are also distinguishable on certain parts of that innermost 

 layer of the general integument which forms the external boundary of the perivisceral 

 space, their action being especially apparent near the ends of those lateral appendages 

 which give support to the pinnulse. By the agency of these cilia a more special move- 

 ment is imparted to the corpuscles of the fluid contained within the perivisceral cavity, 

 than that which they receive from the movements of the body generally, and from the 

 peristaltic contractions of the alimentary canal. Although these corpuscles, which are 

 usually of a spheroidal form and of a diameter of about -g^footh of an inch, very com- 

 monly float singly, they are often to be seen aggregated in smaller or larger numbers 

 into masses, which sometimes attain a considerable size (fig. 10) ; and we cannot doubt 

 that the bodies supposed by Mr. Huxley to be young spermatozoa (p. 359, vol. xxii.) 

 were of this nature. 



We have given much attention to the ciliated canals, first observed by Leuckart and 

 Pagenstecher, which originate in two orifices near the base of the lateral appendages of 

 each side (figs. 7, 8. a, b) on their dorsal aspect, and which then rapidly incline towards each 

 other, so as to converge into a single canal, that runs along for some distance in the wall 

 of the body, and then terminates in the perivisceral cavity (fig. 7. c). One of these orifices 

 {a) is situated in the centre of a sort of rosette*, marked by radiating ridges furnished 

 with large cilia ; the other {b) has round it a smaller rosette, which does not possess any 

 such ciliated ridges. These ciliated canals are obviously the homologues of those which 

 attain so much greater a complexity in the higher Annelida (the " segmental organs " 

 of Dr. T. Williams). Although they are represented by Drs. Leuckart and Pagenstecher 

 as existing in their specimens on every one of the pinnulated appendages, and even in the 

 bases of the second antennae, we can state most positively, both from the observation of 

 numerous living individuals, and from the evidence of well-preserved specimens now be- 

 fore us, that, in the form of Tomojyteris observed by us, they do not exist in the five lateral 

 pairs which immediately follow the second antennae. And this fact is the more remarkable, 

 since, as Avill presently appear, there is a stage in the animal's life at which it does not 

 possess more than five pairs of pinnulated members, and in which, therefore, it is entirely 

 destitute of ciliated canals. The direction of the ciliary current always appeared to us 

 to be from without inwards (as affirmed by Leuckart and Pagenstecher, in opposition to 

 what is generally stated on this point) ; and we repeatedly witnessed the passage through 

 the canals, in this direction, of spermatozoa which had been emitted from the testes into 

 the surrounding water. 



Each of the pinnulae, in our specimens of Tomopteris, presented (fig. 7. d, cl) the peculiar 



* This rosette was noticed by Buscli ; but he onlv imperfectly made out the canal of which it is the entrance. 



