May 19, 1911] 



SCIENCE 



783 



ing the cultures with radium. 



We wish to express our thanks to Mr. Ber- 

 linicke, of the firm of Hugo Lieber & Co., 

 who was kind enough to loan us the radium 

 used in these experiments, and to Mr. Bagg, 

 who assisted us in our observations. 



Jacques Loeb 

 F. W. Bancroft 



EOCKErELLER iNSTITtTTE FOK 



Medical Eeseaech 



y 



AN EXPERIMENT IN DOUBLE JIATING 



In my " Inheritance in Silkworms, I.," 

 (1908)' I called attention (pp. 37-39) to the 

 beginnings of an experiment in double mating. 

 Only the Fi generations following a few ma- 

 tings had been obtained at that time, but they 

 gave such promise of interest that I deter- 

 ■ mined to continue the experiment and to 

 widen it. I have now in hand the notes on 85 

 silkworm broods belonging to this double ma- 

 ting experiment series of 1910. Some of these 

 broods are the Fj generation from the original 

 1907 double matings, while others are F, or F^ 

 generations from the original 1908 or 1909 

 double matings. Taken together the notes of 

 these various 1907-10 rearings from double 

 matings are sufficient to pose some suggestive 

 queries. 



By the double mating of silkworms I mean 

 the mating of a female of one race with two 

 males representing different races, one of themi 

 usually of the same race of the female, the 

 other of another race. Races are chosen which 

 are readily distinguished by a difference in 

 cocoon color, as yellow or white, or in larval 

 pattern, as banded and unhanded. The silk- 

 worm is polygamous and polyandrous, both 

 males and females usually mating more than 

 once before egg-laying begins. Or this re- 

 peated mating may continue after egg-laying 

 has begun. 



Moths to be experimentally double-mated 

 are reared from carefully isolated cocoons, and 



^ ' ' Inheritance in SUkworms, I., ' ' Leland Stan- 

 ford Junior University Publications, University 

 Series, No. 1, 89 pp., 4 plates, 2 text figs., 1908. 

 Address Librarian, Stanford University, Cali- 

 fornia. 



the two matings are made to take place im- 

 mediately following one another for equal or 

 definitely determined unequal periods of 

 coupling, and always before any egg-laying by 

 the female. The young produced from the 

 eggs of each double-mated female are reared 

 isolated in separate trays, which are covered 

 over during the later larval life (possible 

 straggling time). 



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 re- 

 membered. 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 spermathecse, 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 unfertilized eggs of the moth pass 

 slowly down from the ovarial tubes into the 

 oviduct they lack only fertilization to be en- 

 tirely ready for development. They have al- 

 ready their full supply of yolk, they are al- 

 ready enclosed in their protecting envelopes 

 (vitelline membrane and outer, firmer cho- 

 rion). But these envelopes do not completely 

 enclose the egg-mass; there is, at one pole of 

 the egg, one or more small openings, 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 repre- 

 sent a new set of characters. Wliat is going 

 to be the result of this double mating as ex- 

 hibited in the offspring? 



It seems, at first thought, that this result 



