ANIMALS WITH JOINTED FEET-THE ARTHROPODS 



215 



Fig. 11-14. A female crayfish carrying her eggs attached to the swimmerets. The eggs are about ready to hatch 

 because close observation will reveal the embryos just under the shell of the egg. As a matter of fact, these did 

 hatch the following day. 



produced in a tubular testis and pass 

 through the vas deferens to an opening at 

 the base of the fifth ( considering the cheh- 

 peds as the first walking legs) walking legs. 

 An ejaculatory duct toward the end of the 

 tube aids in removing sperm during mating. 

 The first pair of swimmerets is modified in 

 the male to form a copulatory organ for 

 transfer of the sperm to the seminal recep- 

 tacle on the ventral side of the female. 

 The ovaries of the female produce eggs 

 which pass through a straight oviduct to 

 the opening at the base of the third walking 

 legs. Her first pair of swimmerets is rudi- 

 mentary. 



At the start of copulation the male lobster 

 grasps the chelipeds of the female with his 

 pincer-like appendages and turns her over 

 on her dorsal side (Fig. 11-13). The two 

 ventral sides then come together. The first 

 pair of swimmerets of the male is placed 

 near the opening of the seminal receptacle 



of the female and the sperms are dis- 

 charged. The female receives the sperms in 

 packets or spermatophores. 



The female lobster lays eggs only once 

 in two years, usually at the time when the 

 water has reached its summer temperatures 

 (from about mid-June to September 1st). 

 The male, however, is unable to discern the 

 sexual condition of the female and copula- 

 tion often occurs long before the matura- 

 tion of eggs in the ovary. In such cases the 

 sperm cells, which are stored in the seminal 

 receptacle of the female, must maintain 

 their vitality for a long time, very often for 

 several months. Eggs are fertilized after 

 their ejection from the oviducts. As the eggs 

 are extruded, a mucous material is pro- 

 duced by glands in the swimmerets which 

 glues the eggs to the many bristles on these 

 appendages. The eggs are thus carried by 

 the female from ten to eleven months (see 

 Fig. 11-14 where a crayfish is carrying her 



