TRITONIA. 



towards the right side in front of the heart : it then dips down and terminates in an anal 

 nipple situated about midway along the side immediately below the mantle. The alimentary 

 tube is longitudinally plicated throughout ; in the stomach the plicae are strong and much 

 wrinkled. 



The liver (/) is a large pyriform body with the obtuse end forward and hollowed for the 

 reception of the posterior portion of the stomach. The left side is much prolonged, forming 

 a lobe which advances a considerable way forward. The colour is a yellowish rose, caused 

 chiefly perhaps by the ovary which envelopes the organ. The hepatic fluid enters the 

 posterior end of the stomach by a single large duct. ' 



The alimentary system varies only a little in T. plebeia, in which the oesophagus is dilated 

 into an anterior stomach or crop ; and the stomach itself is almost concealed by the liver, the 

 anterior lobe of which is large and passes quite in front of it. The gastric organ has therefore 

 the appearance of lying in a transverse cleft. 



The reproductive organs seem to be arranged more on the plan of Eolis than of Boris. 

 They are composed of the usual three parts, — male, female and androgynous, which open into 

 a common vestibule having a single outlet on the right side of the body, about half way 

 between the head and the anal nipple. The intromittent organ (fig. 2k), which is situated in 

 front of the other parts, is long and tapering ; and the testis (/), a convoluted tube of no great 

 length, is connected with it by one extremity and by the other to the oviduct. The ovary is 

 firmly attached to the liver over which it is spread. The oviduct, at first very delicate (n), 

 dilates and forms a widish tube (m), a little convoluted. Before reaching the testis it 

 contracts to its former diameter, and after its junction with that organ, it suddenly turns upon 

 itself and sinks into the mucus-gland (o, o). This latter organ, like that of Eolis, is very bulky, 

 and is formed of two lateral masses made up of convoluted tubes, which open into the female 

 channel (p). The androgynous apparatus is very simple, being composed of a mere elongated, 

 pyriform sac, or spermatheca {q) terminating a rather short vaginal tube (r). This tube 

 opens as usual into the common vestibule above and between the male and female orifices. 

 There is here no accessory spermatheca nor special duct leading from the androgynous parts 

 to the oviduct as in Doris. The seminal fluid hoarded in the spermatheca must, therefore, 

 pass again down the vaginal tube, and fertilise the ova as they pass out ; or it must find its 

 way by the same tube into the female organs ; in which case it will penetrate the oviduct and 

 perhaps reach even as far as the ovary. 



The generative organs are a little modified in T. plebeia, in which the testis is composed 

 of two portions ; one thin and tubular, the other a little enlarged and fusiform. From the 

 inner extremity of this latter portion, a constricted duct leads to the oviduct, the dilated part 

 of which is very wide and doubled upon itself. The spermatheca is large and oval ; the 

 vaginal tube short and distinct. 



The organs of circulation differ in some respects from those of other Nudibranchs. The 

 heart as usual lies immediately below the dorsal skin, about half way down the body, and is 

 enclosed within a delicate, transparent pericardium, which extends the whole width of the 

 back (fig. \,j). The ventricle (k) is strong and muscular, with the sides much produced, 

 giving it externally very much the appearance of being composed of two chambers. The 

 aorta passes from the frontal apex, and gives branches to the various organs. The auricle (/) 

 is comparatively delicate ; it is narrow, transversely elongated, reaching from side to side of 



