MUSEUM OF COMPARATIVE ZOOLOGY. 6 



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

 forward covering tlie 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 AVatase. 

 Mr. H. H. Field and Mr. Carl H. Eigeumann 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. Xicker- 

 son and Company, of Charlestown, Mass. 



If et hods. 



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 hsematoxylin. 



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 Sehallibaum'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 fiiilm-e 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 mini;tcs. 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 



