No. 606] SHORTER ARTICLES AND DISCUSSION 379 



they are abundant near low-water level. Moreover, I have ob- 

 tained the egg masses in dredgings at every season of the year; 

 hence we may regard the fact of egg laying at all seasons under 

 laboratory conditions as of significance in this connection. The 

 eggs, which are quite characteristic in appearance, and hence 

 easily identified, have been collected in depths of eight fathoms 

 and more. Large individuals of C. zebra are likewise not un- 

 common at these depths ; in fact, the first ones to be described 

 were dredged from ten fathoms in Harrington Sound (Heil- 

 prin, 1889, p. 187). A further point of considerable significance 

 is found in the fact that these nudibranchs, unlike Elysia and 

 certain other species, do not appear to deposit any egg masses 

 upon the "eel grass" 011 which the animals occur in such great 

 numbers throughout the early summer. The egg strings found 

 in the field are invariably attached to rocks, or to the shells of 

 Area noe, the "mussel" with which the adults are frequently 

 associated. The gelatinous egg-ribbons (cf. Smallwood, 1910) 

 are quite large, measuring usually 120 to 150 mm. long by 15 to 

 17 mm. broad, and are much too heavy to be supported by a 

 blade of "eel grass," as can readily be determined by trial. It 

 is only rarely that an egg mass has been obtained in shore col- 

 lecting. 



The migration of C. zebra into shallow water cannot, then, be 

 directly connected with reproductive activities. Since, in the 

 laboratory at least, they deposit eggs usually within twenty-four 

 hours after pairing, it does not seem to me probable that these 

 nudibranchs pair to any great extent during the time which they 

 appear to spend in the tidal "creeks" 110 eggs, as stated, 

 having been collected from among the "eel grass," nor were any 

 ever obtained on the muddy bottoms of these "creeks." Chro- 

 modoris seems to require a firm, hard substratum for the attach- 

 ment of its egg-ribbon. If individuals obtained in quite shallow 

 situations are kept singly in aquaria they sometimes deposit 

 after several days fragments of egg- jelly containing several 

 dozen unfertilized eggs, while they almost invariably pair readily 

 when given the opportunity. Nevertheless, it should be stated 

 that the nudibranchs usually do not occur singly, two or three 

 being commonly found within a space of several square meters 

 even when the total number of individuals in a given area is 

 small; and I am well aware that laboratory findings with regard 

 to breeding habits are liable to be misleading. The established 



