THE CRAYFISH 135 



The Reproductive System. The male reproductive organ, 

 the spermary (Fig. 67, 37), and the female reproductive organ, 

 the ovary, lie just below the heart ; each consists of a three- 

 lobed organ. In the male a sperm-duct (Fig. 67, 38) leads from 

 either side of the spermary to an opening (Fig. 67, 39) on the 

 basal segment of either fourth walking-leg. In the female the 

 oviducts lead to similar openings on the second walking-leg. 



Development. Cambarus affinis lays its eggs in the spring. 

 Most species of crayfishes lay their eggs then. The princi- 

 pal burrowing species, Cambarus diog'enes, lays its eggs in 

 April and they hatch in May, while a river species, Cambarus 

 immu'nis, lays its eggs in the fall and they hatch in the fol- 

 lowing spring. When the egg-lay ing season arrives the male 

 deposits spermatozoa in a shallow cup called the annulus, on 

 the ventral surface of the female, between the fourth pair of 

 legs. The mass of spermatozoa stays in the annulus till the 

 female lays her eggs. It is not certain how long the sper- 

 matozoa lie there before the eggs are laid. However, when 

 the eggs are discharged from the oviduct they pass back over 

 the mass of spermatozoa. Fertilization is accomplished when 

 a spermatozoon enters an egg. The fertilized eggs are carried 

 back and fastened to the swimmerets by a glutinous substance. 

 There the embryos develop, and the larvae, when they hatch, 

 remain clinging to the female's swimmerets by their cheli- 

 peds for some time, probably several weeks. 



Relation to Environment. Crayfishes live in a great variety 

 of places. They are fresh- water animals, but one species has 

 also been found in the sea. As a rule, they crawl on the 

 bottom of rivers, brooks, and ponds, concealing themselves in 

 crevices or under protecting pieces of rock or submerged logs. 

 Several species make burrows in the soft earth of meadows. 

 The most widely distributed of these is Cambarus diogenes. 

 Species which live in ponds that are likely to dry up in the 

 summer, and also a few that live in rivers, leave the water 



