DOUBLE MATING. 



In connection with the question of prepotency of strain or race in 

 cross mating, experiments have been begun in double mating, that is 

 in pairing a female of one race with two (or more) males representing 

 two different races. The silkworm is polygamous, both males and 

 females usually mating more than once before egg-laying begins. Or 

 this repeated mating may continue after egg-laying has begun. 



In any consideration of the results of such repeated mating the 

 unusual way in which the eggs of insects (at least of the silkworm 

 moth and hosts of others ) are fertilized must be remembered. This way 

 is, simply, that the male fertilizing cells, the spermatozoa, are received 

 by the female at mating into a special sac or receptacle, the spermatheca 

 ( there may be several spermathecae, as in flies) in which the spermatozoa 

 remain alive and active. This spermatheca, a diverticulum of the 

 oviduct, is situated near its external opening, the vagina. As the un- 

 fertilized eggs of the moth pass slowly down from the ovarial tubes 

 into the oviduct they lack only fertilization to be entirely ready for 

 development. They have already their full supply of yolk, they are 

 already enclosed in their protecting envelopes (vitelline membrane and 

 outer, firmer chorion). But these envelopes do not completely enclose 

 the egg-mass ; there is, at one pole of the egg, one or more small open- 

 ings, the micropyle, through which the spermatozoa, issuing from the 

 duct of the spermatheca as the eggs pass, enter the eggs. As soon as a 

 single spermatozoan has entered, a jelly-like substance closes the 

 micropyle and prevents polyfertilization. 



Thus when the silkworm moth first mates she receives in her 

 spermatheca, and holds there, a considerable number of spermatozoa 

 representing the heritable characters of the male involved. When 

 she couples again she receives another lot of spermatozoa, and if the 

 second coupling is with a male of different race from the first these 

 spermatozoa represent a new set of characters. What is going to be 

 the result of this double mating as exhibited in the offspring? 



In 1905 a female of Japanese White race (white patterned larva, 

 white constricted cocoon) was mated with a male of the same race and 

 allowed to lay some eggs and was then mated again, this time with a 

 male of Italian Salmon (from a zebra larva) and allowed to lay another 

 lot of eggs. All the larvae (1906 rearings) from both sets of eggs 



