EMBKYOLOGV OF CLEPSINE. 223 



in contact with the spermatozoa after falling from the egg- 

 string. 



I have found that eggs taken from the ovary at the time they 

 are about to be laid develop in the normal maiiaer, and have 

 taken advantage of this to watch the earliest changes in the ripe 

 egg. I liave done this many times, and always with success. I 

 regard this as very strong evidence that impregnation takes 

 place while the eggs are in the ovary. This is in harmony with 

 the fact that I have found spermatozoa in the ovary two or 

 three days before the time for depositing the eggs. It is barely 

 possible that these spermatozoa found their way into the ovary 

 accidentally during the dissecting. I can only say that no 

 testicular sacs were ruptured during the process; but the vasa 

 deferentia may have been severed, as they are so minute that 

 one cannot easily see them. Tlie unchanged condition of the 

 germinal vesicle at the time the eggs have attained their full 

 size renders it probable that fecundation does not take place 

 more than four or five days at the longest before the deposit; 

 but this does not prove that copulation may not have taken 

 place at a much earlier date. I isolated a worm which had just 

 sucked itself full of blood, and which showed no signs of eggs 

 through the body-wall, and after fifteen days obtained eggs that 

 developed in the usual manner. Recalling the fact that the 

 growth of the egg from the primary egg-cell requires only twelve 

 to fifteen days, it appears that this sj)ecimen was isolated about 

 or just before the time when the egg-cell began to grow. lu 

 another case eggs were obtained at the end of twelve days which 

 developed in the normal way. 



These facts have only a negative bearing, but they raise a 

 suspicion that Clepsine is capable of self-fecundation. The 

 question as to whether a copulation occurs will be most satisfac- 

 torily settled by isolating young individuals and keeping them 

 till they produce eggs.^ 



' May 2/1(1, 1S7S. — Five individuals were isolated in the summer of 

 1877, at the time of hatching. Each has been kept in a separate vessel 

 from that time to the present. Eggs were laid by one April 24th (this 

 year), and hatched May 1st ; by two others, April 29th. The latter arc 

 now in the germ-band stage. The water in the vessels was changed in 

 November, March 1, and April 1. The water was taken from a small pond 

 in which these worms are not numerous, and at a time before eggs begin 

 10 be laid by either species. The eggs had in each case passed the pronu- 

 clear stage, at the time they were first noticed, so that I was unable to 

 demonstrate by section the existence of a male pronucleus. As the eggs 

 developed in the normal manner, it is very probable that they were fecun- 

 dated. Here is an unquestionable case of self-fructification, or of partlie- 

 nngenesis — more probably the former. V. Baer ('Miill. Arch,' 1835, p. 

 224) saw strung indications of self-fructificatiou among "hermaphrodite 

 snails." 



