2 TECTIBRAXCHIATA. 



the Opisthobranchiate Orders the blood arrives at the 

 heart more or less obliquely from behind forwards, and 

 the auricle is usually situated behind the ventricle ; the 

 respiration is effected by the aid of arborescent or 

 fasciculated gills, which are never enclosed in a special 

 cavity, but are more or less completely exposed on the 

 back, or at the sides, towards the hind part of the body ; 

 the cervical region, moreover, is entirely naked; the 

 reproductive apparatus is hermaphrodite, the male and' 

 female organs being found in the same individual, and the 

 shell, well-developed in the larva, becomes rudimentary, 

 or even entirely disappears, in the adult animal. 



Order TECTIBRANCHIATA. 



Gill forming a tuft or plume on the side, towards the 

 hind part of the body, under a fold of the mantle, and 

 usually protected by a shell. Both the adult animal and 

 larva shell-bearing. Foot elongate, formed for walking. 

 Marine. 



Observed under favourable circumstances in their 

 native haunts, the Tectibranchiate Mollusks are by no 

 means unattractive or sluggish in their habits, but contri- 

 bute, by their changing forms and lively colours, to lend 

 animation to the weedy shores and coral reefs among 

 which they take up their abode. The Bulla, there no 

 longer a shapeless mass of blubber, expands its fleshy 

 foot-lobes and floats leisurely through the water; and, 

 crawling on the rocks above the ripple of the sea, the 

 green, amphibious Smaragdinella may be observed 

 probing the surface with its plastic head-disk. Gliding 

 along the surface of the slimy mud, the Pleurobranckus 



