HOMARUS AMERICANUS MILNE-EDWARDS 135 



of the stylets. These are the first pair of pleopods specially 

 modified for the purpose of copulation. The endopodite of the 

 second pleopod has a short spur and the median spines of the 

 abdominal sternites are fully developed. A pair of testes, some- 

 times separate, sometimes united by a transverse bridge, are 

 situated behind the heart, partly concealed by the liver. The 

 sperm duct or vas deferens of each testis is a coiled up tube. Its 

 muscular end portion functions as a ductus ejaculatorius. The 

 sperm cells are provided with three stiff rays and are immobile. 

 They are very complicated structures designed to " explode" 

 on touching the egg. 



Female. The openings of the oviducts are on the coxopo- 

 dites of the third pair of pereiopods (i2th somite) and are di- 

 rected backward and inward. The sternite of the fourteenth 

 somite is modified as a sperm receptacle and serves as an organ 

 of copulation and for storage of the sperm. The median spines 

 of the abdominal sternites are poorly developed. The first 

 pleopods are small and filiform, the endopodite of the second 

 pleopods lacks the spur present in the male. A pair of ovaries 

 connected by a traverse bridge occupy in the mature female 

 all the space on each side of the body from the stomach to the 

 fourth or fifth abdominal somites. The oviducts are compara- 

 tively short tubes. The number of eggs increases with the age 

 and size of the animal and reaches the total of about one hundred 

 thousand in females of over fifteen inches in length. In spawn- 

 ing the female lies on her back and as the eggs leave the oviducts 

 and pass by the sperm receptacle, they are fertilized; each egg 

 becomes inclosed in a thin capsule; the eggs adhere to each 

 other and the whole batch is carried by the mother attached to 

 the pleopods. Development is indirect, combined with a meta- 

 morphosis. 



Instructions 



i. Examine the dorsal surface of a lobster and make a full 

 page drawing of it, labeling all parts mentioned below. 



