130 



CHAS. B. WILSON. 



It follows tlmt the eggs must be fertilised outside the body 

 of the female^ and that the sperms often have a considerable 

 distance to travel before reaching the eggs. This will account 

 m part for their very strong motion^ and it also verifies the 

 statement made by Coe (15) that all the genital products are 

 not discharged at once, but only a limited portion of them. 

 From the fact that the several lots of eggs were laid so near 

 together, it seems probable that the period of egg-laying in 

 any one individual does not occupy more than a week or ten 

 days. When Nemerteans are kept in confinement without 

 any chance to burrow, they usually pull themselves in pieces 

 after a short time. If the sexual products are ripe when this 

 occurs they are always discharged, and perfectly healthy 

 fertilised eggs may often be obtained in this way. 



Darwin, in his ' Descent of Man,' says that these animals, 

 like many other Invertebrates, " apparently stand too low in 

 the scale for the individuals of either sex to exert any choice 

 in selecting a partner, or for the individuals of the same sex 

 to struggle in rivalry." This is undoubtedly true, but we 

 must remember with Mcintosh that this does not exclude 

 the possibility of a very delicate sexual instinct. The simple 

 fact that the sperms are discharged simultaneously with the 

 eggs, even though the burrows of the male and female may 

 be some distance apart, proves the existence of such an in- 

 stinct. 



Fertilisation and Ripening. 



There is nothing resembling copulation, eggs and sperm 

 being discharged fi*om separate burrows. When ripe the 

 eggs fertilise almost immediately, but with a little care the 

 entrance of the sperm into the egg may be seen, though its 

 subsequent action must remain invisible owing to the opacity 

 of the yolk granules. A great many sperms usually pene- 

 trate the limiting membranes, but only one of them enters 

 the Qgg, though instances of polyspermy are not unknown. 

 The sharp curved point of the sperm is placed against the 

 surface of the egg, and a gentle vibratory movement is pro- 



