176 



THE MORPHOLOGY OF THE COMMON CRAYFISH. 



of the body consists of one or more of the following eight 

 histological groups : — 



1. Blood corpuscles; 2. Epithelium; 3. Connective 

 tissue; 4. Muscle ; 5. Nerve; 6. Ova; 7. Spermatozoa; 

 8. Cuticle. 



1. A drop of freshl_y-drawn blood of the crayfish con- 

 tains multitudes of small particles, the blood corpuscles, 





10 ^^ 



Vl5 



^l 



Fig. 40. — Adacns fnrinfilig.—The corpuscles of the blood, higlily 

 magrnified. l^S, show the changes undergone by a single cor- 

 puscle during a quarter of an hour ; «, the nucleus ; and 10 

 are corpuscles killed by magenta, and having the nucleus deeply 

 stained by the colouring matter. 



which rarely exceed l-700th, and usually are about 

 1-lOOOth, of an inch in diameter (fig. 49). They 

 are sometimes i:>ale and delicate, but generall}' more or 

 less dark, from containing a number of minute strongly 

 refracting granules, and thej' are ordinarily exceedingly 

 irregular in form. If one of them is watched continu- 



