506 



H. H. SWINNERTON. 



For material used in investigating general questions 

 arising out of the study of the stickleback's skull, I have 

 relied upon the teaching collection of the Royal College of 

 Science, on a series of microscopic preparations which 

 were given to the College by the family of the late Dr. 

 Pollard, and on the fish skeletons now being incorporated 

 in the collections of the British Museum of Natural History. 

 The first two of these were kindly placed at my disposal by 

 Professor Howes, and the last by Mr. Boulenger. 



The methods pursued were the same as those used when 

 investigating the skeletogeny of Sphenodon in conjunction 

 with Professor Howes (01) ; and as they are described with 

 some detail in our memoir on that animal, I shall not repeat 

 them here. 



For embryonic, larval, and young material I found 

 Perennyi's fluid more useful for fixing purposes than either 

 picro-sulphuric or corrosive sublimate, because it was less 

 liable than these to bring about distortion. 



For adults 4 per cent, formalin was used. 



III. Descriptive and Comparative. 



' The Cranium. 



Stage I. — Up to the end of the fifth or even early on the 

 sixth day the only definite representative of the skeleton in 

 i\\e head of the stickleback is the notochord, the cells of 



