STRUCTURE OF THE LARVA OF SPONGILLA LACUSTRIS. 441 



The specimens when first put in floated in the intermediate 

 layer, but gradually sank to the bottom. The liquid above 

 them was being continually drawn away with a pipette, so 

 that by the time they had sunk to the bottom they were in 

 almost pure chloroform, after which they were transferred to 

 the pure liquid. 



After the specimens had been brought into pure chloroform 

 they were transferred into small watch-glasses, which con- 

 tained some chloroform together with a certain amount of 

 high-melting paraffin (135° F.), and were placed on top of the 

 water-bath. The chloroform soon evaporated, and the paraffin 

 simultaneously melted. They were then placed in the water- 

 bath, where the last traces of chloroform were driven away. 

 They were left in the water-bath only for a very short time, in 

 order that they might not be subjected to high temperature 

 for a long interval, which is an important thing if histological 

 details have to be considered. 



The paraffin used for embedding was that which melts at 

 135° F. 



The sections were always cut with a Jung microtome, the 

 block being painted over with a mixture of collodion and gum 

 mastic dissolved in ether when exceptionally thin sections were 

 required. The usual thickness was about 3 fx, though sections 

 varying from 2^ to 6 )u were occasionally cut. 



So many methods of staining have been tried, that it would 

 be going too far even to enumerate them all. However, the 

 most important and generally useful in connection with the 

 development of Spongilla will be given. 



(a) Borax Carmine followed by Bleu de Lyon. — This 

 is a most important method, as it has been used by previous 

 observers, and has given diflferent results in different hands. 

 The staining of the specimens with borax carmine has already 

 been described ; there is therefore no need but to give the 

 last part of the process. Several ways of staining carmine- 

 coloured sections with bleu de Lyon have been tried, but the 

 following has proved to be the most useful. The sections 

 were overstained with carmine, and could on that account be 



