TRIOPA. 



The body of Triopa is elongated and rather depressed, tapering posteriorly. The cloak 

 is small, exposing the foot, rounded and extended over the head anteriorly, and terminating 

 m a point behind. Its margin is adorned with numerous linear, subclavate processes. The 

 head is inferior, with two shortish labial tentacles : the mouth is not furnished with jaws. 

 The two dorsal tentacles are laminated and retractile within small sheaths. The branchiae 

 are plumose, generally few in number, and placed immediately in front of the vent, partially 

 surrounding it at the base, on the median line of the back. The foot is moderately" sized, 

 nearly linear, and deeply sinuated in front. The aperture of the genital organs is simple, 

 situated on the right side about one third down the body. 



Our observations on the anatomy of this genus must be confined to that of T. claviger, 

 the only one we have had an opportunity of dissecting. 



The buccal organ is rather small, and less muscular than usual ; thl channel leading to 

 it from the external opening, which is situated on the under surface of the head, is very 

 short: there are neither jaws nor prehensile collar, and the tongue is formed on the type of 

 that of Polycera, but is somewhat broader; it is of a pale yellow colour, and is divided down 

 the centre by a naked space : the tubular portion behind projects, slightly from the posterior 

 end of the buccal organ. The plates are numerous and are arranged in about forty-five rows 

 of twenty-two plates each ; the ten external ones are much depressed, of a square form, and 

 set close together ; the two on each side of the median line bear large curved spines, the 

 innermost being much attenuated, the other very stout and with a single denticle near the 

 point.* 



The oesophagus, which is of no great length, passes from the buccal organ above and 

 behind, and has at its origin a pair of tubular salivary glands, which open into the mouth in 

 the usual way. At first the alimentary tube is much constricted, but immediately on passing 

 through the nervous collar, it is suddenly enlarged a little, and soon afterwards contracting 

 slightly, is continued backwards, of equal caliber, to the anterior border of the liver, into 

 which it plunges, the stomach being buried in that viscus. The intestine is short ; it issues 

 from the upper surface of the hepatic organ towards the left side, and, passing across 

 towards the right, pursues its path, almost in a straight line, to the anus. 



The reproductive organs are similar to those of JEgirus. The glandular portion of the 

 testis and the spermathecse are, however, somewhat modified in form. The oviduct too is 

 rather peculiar : at first it is much attenuated and then, as usual, becomes suddenly and 

 much enlarged ; but afterwards contracts again at a considerable distance from its junction 

 with the testis. The ovary covers the upper surface of the liver, giving to that organ a very 

 distinct tesselated appearance : it is composed of a number of large globules surrounded by 

 smaller ones; the latter are yellowish, and contain ova; the former are pale in colour, and 

 filled with spermatozoa. 



The vascular system does not appear to differ from that of the other Polycerince, — the 

 pericardium, ventricle, auricle, and portal heart exhibiting no peculiarity. The renal organ 

 has not been observed. 



* We have had an opportunity of examining the buccal organ of Euplocamus croceus, which differs 

 from that of Triopa claviger in having a prehensile collar, and a much broader tongue, with very 

 numerous plates ; three of the inner ones on each side bear large blunt spines. 



