554 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
described a case (: 01 , p. 74) in which about 50 sexually mature 
individuals of Micrura alaskensis , some of which were 300 mm. in 
length, were coiled and twisted together in a single mass. This 
exaggerated gregarious instinct is doubtless associated with the 
reproductive processes. 
That the deposition of genital products by one sex often excites 
the other sex to a corresponding act is attested by the observations 
of C. B. Wilson (: 00, p. 128), who noticed that when several sexually 
mature worms of both sexes are placed together in an aquarium the 
deposition of ova by one individual is often accompanied by the 
discharge of spermatozoa by another, even though the burrows of 
the two worms may be separated by a considerable space. These 
observations certainly indicate, as Wilson asserts, the existence of 
some sort of delicate sexual sense among the nemerteans. 
Development. 
So far as is at present known the eggs and spermatozoa mature 
in the late spring and early summer, the fully developed young 
worms being discharged from the body in midsummer. The period 
of sexual maturity, however, as stated above, may possibly continue 
later in the year, although no observations have been made in the 
fall months. The exact time required for the completion of the 
developmental processes has not been determined because there is 
considerable variation in the time at which the eggs reach maturity 
in different individuals. There is little doubt, however, that a 
period of several weeks elapses between the time of fertilization of 
the eggs and the appearance of the young worms outside the body 
of the parent. In Geonemertes ctustrciliensis , the eggs of which are 
deposited immediately after fertilization, a period of several weeks 
is required to complete the development of the embryo. On the 
26th day after the ova had been deposited, Dendy (’93, p. 130) 
found a portion of the embryos nearly ready to crawl about, 
although others were as yet within the egg membranes. At least a 
month seems to be required for the development from the time of 
fertilization to the arrival at the elongated, worm-like form provided 
with ocelli. 
The details of the process of fertilization have not been observed, 
nor has the cleavage of the egg been followed through all its 
