Note on the structure and relations of the kidney in Aplysia. 427 



extent, tili these organs lie ou the right side. What is known of the 

 development of Nudibranchs indicates that they are to be derived from 

 fornis similar to the Anisobranchia (or Ctenobranchia in Claus' Zoo- 

 logie) among the Prosobranchiata. Unfortunately little is known of the 

 Position of kidney, gill and rectum in the young stages of Aplysia or 

 other forms among the Tectibranchiata ; but from the appearance of the 

 embryo it seems probable, that the relations of these parts in the latter 

 are similar to those which obtain in the adult Anisobranchia, and 

 that in the course of growth an actual untwisting takes place, which 

 carries the organs from the anterior dorsal surface to the right side. 



Explanation of Figures. 



Piate 30, 



Fig. 1 . Dorsal surface of Aplysia depilans ; the epipodìa have been cut away 

 along the line e}), the shell cavity has been opened and the shell removed, 

 and the pericardium laid open. 

 k kidney. 

 mf fold of the mantle which lies above the shell. 

 si tubulär Prolongation of mantle, or siphon. 

 m free lobe of the mantle. 

 sg seminai groove. 



rp depression containing the opening from pericardium into kidney. 

 Fig. 2. View of the branchial Chamber of A. depilans. The free fold of the mantle 

 has been drawn as far as possible to the right side so as to expose the 

 Chamber completely, and the branchia has been cut away. 

 h kidney. 



eo external opening of kidney. 

 an anus. 



pg area covered by openings of poison glands. 

 go genital opening. 

 sg seminai grove. 

 si siphon. 



ol olfactory organ of Spengel. 

 Fig. 3. Section of kidney perpendicular to the dorsal surface and to the face 

 bordering the pericardium. The section passes through the canal leading 

 from the pericardium to the cavity of the kidney. Zeiss aa. 

 pc pericardial cavity. 

 he cavity of kidney. 

 ci connective and muscular tissue. 

 hi blood lacuna. 

 ke kidney epithelium. 

 rpc renopericardial canal. 



