382 - Multicellular Animals, Especially Man 



%,. 



4 ** 



Fig 21-2. Male brook stickle- 

 back, guarding nest. (Courtesy 

 the New York Conservation 



Department.) 



contains nutrient substances to sustain the secretes a broad beltlike cocoon around its 

 sperm until they make contact with the eggs. clitellum, and starts wriggling backward to 



In most cases a single copulation serves to escape from the encircling girdle. The eggs 

 fertilize only such eggs as happen to be ma- of the worm are extruded into the cocoon 

 ture at that time. However, the lemale repro- when this girdle has been displaced forward 

 ductive tracts of some animals (for example, 

 many birds and insects) displa) one or more 

 blind outpocketings, the seminal receptacles, 

 in which the sperm collect and remain active 

 for considerable periods alter copulation. 

 Thus the cjiieen bee receives just a single 

 visitation of the drone, and yet continues to 

 deposit fertilized eggs for the rest of her re- 

 productive life. Also the domestic hen may 

 lay fertile eggs for a number of months after 

 one contact with a rooster. 



In some hermaphroditic animals, the cop- 

 ulating partners may mutually inseminate 

 each other. For example, when earthworms 

 copulate (Fig. 21-3), both individuals ex- 

 trude semen from the sperm duct openings 

 (segment 15). In each case the semen of one 

 worm is guided into the other's seminal re- 

 ceptacles, two pail ol blind pockets that 

 extend inward from the ventral body wall in 

 the ninth and tenth segments. Thus the net 

 result ol copulation is that the seminal re- 

 ceptacles of each worm become filled with 

 the semen of the other, and actual fertiliza- 

 tion of the eggs does not occur until after the Fig. 21-3. Earthworms, copulating. (Copyright, Gen- 

 partners have separated. Then each worm eral Biological Supply House, Inc.) 



