512 A. iM. CAKK SAUNDEHS AND MAIUIAKKT I'OOLE. 



the surface. The two cerebral ganglia are close together and 

 are united by a broad commissure. Mazzarelli states that 

 cerebro-pedal and pedal commissures are present. We have 

 been unable to discover these. The velum and foot are at 

 this stage full of connective tissue, and it would be difficult 

 to trace a fine commissure if it did exist. Visceral ganglia 

 are absent at this stage of development. 



The Secondary Kidney. — In making use of the term 

 '' secondary kidney " we are following the nomenclature of 

 Mazzarelli. In his study of the free-swimming larvae of 

 Opisthobranchs he gives this name to the unpaired right 

 kidney, which he has shown to be characteristic of all these 

 larvfB. The term " primitive kidney " he reserves (and we 

 follow him in doing so) for the smaller paired kidneys, the 

 nephrocysts of Trinchese, which lie anteriorly to the '•'secon- 

 dary kidney " at the base of the velum. It is necessary to make 

 this clear, since owing to the nomenclature used in Carazzi's 

 recent work confusion may arise. In the earliest stage with 

 which we deal we have already described four lai-ge ectoderm 

 cells, and have said that they would give rise to the secondary 

 kidney. Now Cai-azzi mentions these cells and identififS 

 them as 3c"", 3c"'~, 3r'-", and Sc^-^\ We have no doubt that 

 these four cells are the same as those which we describe and 

 figure. But Carazzi in his table of the cell lineage marks 

 these cells as giving rise to the " reni primitivi." In the 

 text all he savs with reference to the fate of these cells is : 

 " Una parolo devo aggiungere sul desterio delle grandi 

 cellule or^^^^ 3c"^- ; esse constituiraniio uno dei primi organi 

 emissionali, cive il rene primitive. " It is quite impossible 

 from this to understand whether, as one would incline to 

 think from the quotation cited, Carazzi calls primitive kidney 

 what we call secondary kidney, or whether, from the fact 

 that in the table of cell lineage he says these cells give rise 

 to " reni primitivi '' (in the plural), he has not made the 

 mistake of thinking that the cells in question are the rudi- 

 ment of what we call primitive kidneys, and not of what we 

 call secondary kidneys. 



