286 W. J. CROZIER 



2, Size. It is said that many nudibranchs die soon after de- 

 positing eggs (Eliot, '10, p. 18). These animals are often sup- 

 posed to live for but one year, passing through a single breeding 

 season. The life history of Aplysia is said also to be of this sort 

 (Storrow, '15). Available knowledge of the life histories of 

 marine animals is far too fragmentary to allow of much generali- 

 zation, but as a rule this particular kind of life cycle seems 

 typical of species exliibiting a restricted period of breeding in- 

 itiated by some special kind of behavior (e.g., the case of the 

 medusa Linerges; Conklin, '08); in many of these instances the 

 mature animals are all of about the same size. 



With Chromodoris zebra I find it difficult to believe either that 

 the individuals live but one year, or that they breed but once. 

 The size frequency distribution is practically identical through- 

 out the year. It is true that, after depositing eggs, some indi- 

 viduals quickly succumb when confined in aquaria; it is also 

 true, however, that specimens of lengths ranging from 4 to 17 

 cms. will, even in the absence of food, live in the laboratory for 

 several months after they have first deposited eggs, during which 

 period they usually lay several additional egg ribbons. The 

 several moribund specimens which I have been able to discover 

 in the field were each 14-16 cms. long. Provided the idea were 

 correct that C. zebra is an annual, and that the size variation 

 could not wholly be accounted for on the basis of the amounts of 

 food assimilated in different cases, then it might be necessary to 

 fall back upon the conception of "pure lines" possessing differ- 

 ential genetic factors for size, as in Paramecium. In this event, — 

 which is, however, highly problematical, — assertive pairing would 

 have the effect ascribed to it in Paramecium (Jennings, 'lib), 

 namely that the boundaries of the several 'pure lines' would 

 through this influence tend to be perpetuated and maintained as 



number of eggs or embryos contained in a single female increases with the size 

 of the animal; the larger females are said to mature earlier than the smaller ones. 

 But conjugation with males (which are smaller than the female) occurs in June 

 or early July, whereas the eggs are not fertilized, at the earliest, until the ensu- 

 ing December. This may, I believe, be regarded as one of those instances in 

 which part at least of the apparatus essential for highly "purposeful" behavior 

 seems to be available, yet remains unused. 



