No. 447-] BREEDING HABITS OF CRAYFISH. 187 



recognizable upon the egg and moreover the egg is 250 times as 

 thick as the sperm and quite opaque. 



The whole process of sperm and egg-meeting and union is 

 much in need of elucidation. 



Sperm. — While the pairing habits of Cambarus are more 

 complex than those of Astacus the sperm cells are not as com- 

 plex in form as those described for Astacus by Herrmann. 

 In place of the many radiating arms he figures C. affinis has six, 

 as a rule, but sometimes 5, 7 or 8. This is also true 

 of C. bartoni. The remarkable bowl shaped vesicle of the 

 crayfish sperm does not have as complex a shape in either 

 of these American forms as it has in Astacus. The diameter 

 of the body is 8 /x while the arms extend out four times that 

 distance on every side so that the entire spread of arms is 

 over 70 ; but only the refractive vesicle is conspicuous and 

 its longest diameter is less than that of the body. 



Period of development, — Attached to the pleopods and 

 presumably fertilized the eggs go through the developmental 

 changes that have been described for Astacus by Reichenbach 

 and others. As these specimens of C. affinis were kept in con- 

 finement the times of various phenomena could be determined 

 with some precision and in general the eggs of any female 

 develop at about the same rate while the eggs of different 

 females progress differently. Eggs laid near the end of March, 

 1894, and in 1900, hatched late in May : eggs laid April nth, 

 1901, hatched the end of May. In 1903 eggs were laid from 

 March 23d to April 15th; when the eggs were kej^t in water 

 at i2j° to 14° c some required eight full weeks to h;itch ; others 

 in a warmer room where the water was not constantly running 

 hatched in six weeks, and some in just five weeks. Most were 

 hatching about May i8th and this was true also of eggs on the 

 females taken April 20th and then in late cleavage or even 

 embryonic stages ; so that it seems probable that late in May 

 is a natural time for hatching in the open where these crayfish 



Cleavage. — The nuclear multiplications and migrations 

 of " cleavage " take place but slowly in this heavily yolk laden 

 egg. From sections it seems that the sperm and egg nuclei may 



