AN EXPLANATION OF THE NON-PRODUCTION OF 

 FERTILIZED EGGS BY ADULT MALE-PRO- 

 DUCING FEMALES IN A SPECIES OF 

 ASPLANCHNA. 



D. D. WHITNEY. 



It has been observed by various investigators in the study of 

 certain of the rotifers that in order for a male-producing partheno- 

 genetic female to develop fertilized eggs the female must pair 

 with the male soon after leaving the egg while she is quite young 

 and small. No one has observed the real reason or necessity for 

 this early pairing. 



While working with a species of Asplanchna in the summer of 

 1908 at Cold Spring Harbor, New York, and again in the present 

 summer it has been possible to watch the pairing of the two 

 sexes under the microscope. This species is one that has very 

 large individuals, probably as large as any species of rotifer. 

 Both the female and the male are very transparent, thus making 

 it possible to observe all the internal organs, including the ovaries 

 and the eggs of the female, and the organs of the male with the 

 living sperm in the testis. The sperm are very large and can be 

 easily seen with the. one third objective. When the male and 

 female pair the two individuals come into contact with each other 

 and the male keeping the head pressed against the body of the 

 female bends the body and assuming the shape of a letter U 

 brings the posterior end into contact also with the body of the 

 female. Then the copulatory organ of the male is forced through 

 the cuticle of the female into the body cavity, like a hypodermic 

 needle, and the sperm passing through it are ejected into the 

 body cavity of the female. The sperm immediately become 

 active and, on account of their large size, can be easily observed 

 swimming around in the body cavity of the female. This 

 hypodermic injection of sperm may be made on any part of the 

 trunk region of the female. 



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