MUSEUM OF COMPARATIVE ZOOLOGY. 3 



stages C and D, the abdomen of the embryo is recurved, and reaches 

 forward covering the space between the optic lobes. Stage E corre- 

 sponds to the time of hatching. Stage F is represented by a young 

 lobster one inch in length. 



The younger stages which follow the hatching of the lobster are 

 obtained with considerable difficulty, and I am under obligations to 

 several of my friends for material which covers this period. For some 

 lobsters in the " Schizopod " stage I am indebted to Mr. Sho Watase. 

 Mr. H. H. Field and Mr. Carl H. Eigenmann kindly collected for me 

 some young lobsters one inch in length. From Mr. F. L. Washburn I 

 received the eyes of several half-grown lobsters, six to eight inches in 

 length. The material which I used in studying the histology of the 

 eye in the adult was very kindly supplied to me by A. T. ISTicker- 

 son and Company, of Charlestown, Mass. 



Methods. 



The methods of staining, embedding, etc., which I have employed, 

 are those known to all students of modern histology. In one case, 

 the staining of nerve-fibres, I have used a method which I accidentally 

 discovered while experimenting with Weigert's hematoxylin. 



In employing this method it is necessary to stain the sections on the 

 slide. The way in which I have stained sections on the slide has already 

 been described ('87, p. 175). Further experience has shown, however, 

 that the successful employment of this method necessitates a careful 

 observance of certain precautions. These I have not sufficiently em- 

 phasized in my former account, and I therefore redescribe the method, 

 calling especial attention to the precautions. The method consists in a 

 cautious use of Schallibaum's fixative. The fixative which I have em- 

 ployed is composed of clove oil three parts and Squibb's flexible collo- 

 dion one part. The mixture before being used should be allowed to 

 stand for about a week. After several months it may become ineffective. 

 When working, I usually employ the fixative frequently enough to fol- 

 low its changes, and at the first signs of failure I make a new mixture. 

 If for any reason I have not used the fixative for some time, I test it 

 with a few waste sections before employing it with valuable material. 

 In using it a moderate amount is applied to the slide, and the sections 

 in paraffine are placed on it. The slide and its sections are now sub- 

 jected to a temperature of 58° C. for fifteen minutes. It is important 

 to observe carefully both the length of time during which the slide is 

 heated and the temperature to which it is raised. At the end of fifteen 



