66 



(23) The possession of a paii* of osphradia placed right 

 and left in the nuchal cavity. 



(24) The possession of two kidneys right and left, the 

 left still possessing some excretoiy tissue. 



(25) The extrusion of the sexual products through the 

 I'ight kidney and the absence of all accessory sexual organs. 



Of those characters which are peculiar to the Docoglossa 

 amongst Gastropods — 



No. (12) is an adaptation to the adhesive habit, while 

 (14), (15), and (17) are consequences of the consolidation of 

 the visceral hump involved in the development of (12). 



No. (1(5) is due to the disappearance of the right ctenidium 

 and the subsequent shifting of the heart to the left side so 

 that it might lie behind the remaining ctenidium (which has 

 also disappeared in PafrUa). 



No. (13) is a specialisation enal)ling tlie animal to gather 

 its food by scraping the rock or other surface over which 

 it creeps. 



Among the Cyclobranchs: — 



Nos. (1) and (5) are specialisations to overcome the 

 difficulty of digestion of the tough food. 



Nos. (2) and (7) are special consequences of the further 

 compression of the parts of the visceral hump among these 

 forms. 



No. (3) is an undoubted characteristic, but is not easy to 

 understand, 



No. (4) is an adaptation to the hal)it of extruding the 

 tip of the odontophore for raking purposes and to the 

 consequent need of a Hat dorsal surface, a Ijroad front, and 

 facilities for adjustment. 



The reduction of the pericardium has led to the develop- 

 m ^nt of No. (()), this ari-angement promoting the regnl.ir 

 uid unimpeded circulation of the blood. 



No, (8) is the feature which gives the group of " CVelo- 



