176 THE MORPHOLOGY OF THE COMMON CRAYFISH. 



of the Doay 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 freshly-drawn blood of the crayfish con- 

 tains multitudes of small particles, the blood corpuscles, 



4 





Fig. 49. — Astacus fliiviatilis.— The corpuscles of the blood, highly 

 magnified. 1 — 8, show the changes undergone by a single cor- 

 puscle during a quarter of an hour j n, the nucleus ; 9 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 ahout 

 l-1000th, of an inch in diameter (fig. 49). They 

 are sometimes pale and delicate, but generally more or 

 less dark, from containing a number of minute strongly 

 refracting granules } and they are ordinarily exceedingly 

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



