No. 606] SHORTER ARTICLES AND DISCUSSION 381 



continuance of quiet, still weather is not enough to determine the 

 abundance of Chromodoris in the tidal ''creeks," since they 

 disappear for the most part before the calm summer season is 

 half over. The occurrence of individuals in deep water, together 

 with field observations of specimens which were engaged in creep- 

 ing downward on the sloping sides of rocks and reefs, leads me 

 to doubt very much that any form of geotropic irritability exerts 

 a preponderant control over the normal behavior of these ani- 

 mals. My observations strongly suggest, however, that there 

 does occur to some extent (in appropriate places) a diurnal ver- 

 tical movement of Chromodoris, which is directly determined by 

 the positive phototropism of these nudibranchs. 2 



Specimens of the species known as Chromodoris roseapicta 

 Verrill (there is some doubt that it is really a Chromodoris) 

 have been found in littoral locations, only in the summer time, 

 but this type is not sufficiently abundant to make possible a test- 

 ing out of ideas concerning its migratory movements. 



The point which I wish to emphasize most is the uncertain 

 nature of conclusions having reference to the normal behavior 

 of animals inhabiting the warmer seas on the basis of compari- 

 sons with superficial features of the movements of their rela- 

 tives in colder waters. In the case of Chromodoris zebra, it 

 seems to me definitely established that the periodic flocking of' 

 individuals into very shallow water has no immediate connec- 

 tion with reproduction. 



On Jan. 10th, 1917, I found that C. zebra was crowding in 

 great numbers into the entrance of Fairyland Creek. During 

 the next few clays they became very abundant indeed, so that on 

 one occasion 230 of them were picked up in less than an hour's 

 collecting. On Jan. 12 I began to find egg masses attached to 

 certain sponges, matted algas, mangrove roots, and sundry moor- 

 ing stakes in the "creek." I had not before found any in this 

 place, as stated above. The nudibranchs were observed in copu- 

 lation, and great numbers of egg-masses were found. The at- 

 tachment of the egg-masses was most frequently to some firm 

 object. Within the week Jan. 10-17 they began to disappear, and 

 after a fairly severe storm which came at that time very few were 

 obtainable in the "creek." This occurrence seems to form a good 



2 I am anticipating here the statement of certain facts regarding the re- 

 sponses of C. zebra, which were established in this laboratory several years 

 ago by Dr. L. B. Arey (cf. also Crozier, 1916"). 



