NUDIBRANCHIATA. 



411 



nervous system they show the specialized feature of the reduction of ganglia 

 on the visceral commissure. 



The Dorids are the most specialized of all in possessing the median anus 

 and the triaulic generative ducts ; but they lack the 

 diffusion of the liver. 



The Eolids are highly specialized in their nervous 

 system and cerata, but have the diaulic ducts. Janus, 

 however, goes further in having a median anus, though 

 the kidney is still lateral ; but if we should be tempted 

 to put Janus at the top of our genealogical tree we should 

 be prevented by the fact that in its nervous system it 

 approaches Tritonia, and that it has diaulic generative 

 ducts . 



The Elysiids retain primitive features of the nervous 

 system, but in other respects are the most specialized of 

 the group. But the nervous system drags them down, 

 and would prevent us from putting them at the top of 

 our genealogical tree. Indeed, by it we might feel inclined 

 with Bergh to place them in a separate Tribe between the 

 Tecti- and Nudi-branchiata. 



Section 1. Tritonioidea. 



The liver is contained entirely or principally in the 

 visceral mass. The anus is on the right side. There are 

 generally two rows of branched dorsal appendages. Male 

 and female openings contiguous ; genital ducts diaulic. 

 The heart is asymmetrical, being on the right side. 



Fam. 1. Tritoniidae. Anterior tentacles forming a 

 frontal velum, foot large. Pleural ganglion distinct from 

 cerebral. Kidney a simple sac opening externally on right 

 side above the anus. Two rows of branched cerata without 

 liver continuations. Tritonia Cuv. (Fig. 325), Marionia 

 Vayssiere. 



FIG. 325. Tritonia 

 lineata, dorsal view, 

 X 7 (after Hancock, 

 from Pelseneer). / 

 posterior tentacle ; 

 II dorsal appendages 

 (qerata) ; III eye ; 

 I V frontal velum ; o 

 genital opening. 



FIG. ZZ&.PhyllirUoe bucephalum, from the right side, x 3 (after Sonleyet). The genital ducts 

 are supposed to be a little unrolled. I genital gland ; II sperm oviduct ; III hepatic duct ; 

 IF female genital orifice; V pedal ganglion ; VI salivary gland ; VII mouth ; F/TTstomato- 

 gastric ganglion ; IX buccal mass ; X tentacle ; XI cerebral and pleural ganglion ; XII lobe 

 of liver; XIII heart in pericardium; XIV reno-pericardial opening; XV external opening 

 of kidney ; XVI anus ; XVII liver. 



