38 LOUIS AG AS SI Z. 



fishes of our Swiss lakes. The species Cypri- 

 nus and Corregonus with their allies, including 

 Salmo, are, as you know, especially difficult. 

 I will preserve some small specimens in alco- 

 hol, and, if possible, dissect one of each, in 

 order to satisfy myself as to their identity or 

 specific variety. As the same kinds have re- 

 ceived different names in different lakes, and 

 since even differences of age have led to dis- 

 tinct designations, I will note all this down 

 carefully. When I have made it clear to my- 

 self, I will send you a catalogue of the kinds 

 we possess, specifying at the same time the 

 lakes in which they occur. As I am on the 

 chapter of fishes, I will ask you : 1. What are 

 the gill arches ? 2. What the gill blades ? 3. 

 What is the bladder in fishes ? 4. What is 

 the cloaca in the ^gg - laying animals ? 5. 

 What signify the many fins of fishes? 6. 

 What is the sac which surrounds the eggs 

 in Bombinator obstetricans ? . . . Tell Dr. 

 Leuckart I have already put aside for him the 

 Corregonus umbla (if such it be), but can get 

 no Silurus glanis. 



I suppose you continue to come together 

 now and then in the evening. . . . Make me 

 a sharer in your new discoveries. Have you 

 finished your essay on the physiology of plants, 

 and what do you make of it ? . . . 



