No. 606] SHOBTER ABTICLES AND DISCUSSION 



381 



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

 abundance of Ckromodoris 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 Ckromodoris, which is directly determined by 

 the positive phototropism of these nudibranchs." 



Specimens of the species known as Ckromodoris roseapicta 

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

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

 but this type is not sufificiently 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 Ckromodoris zehra, it 

 seems to me definitely established that the periodic flocking of 

 individuals into very shallow water has no innnediate connec- 

 tion with reproduction. 



On Jan. 10th, 1917, T found that C. zehra was crowdiiiir in 

 great numbers into tlie fiitriiiin' df Fairyl.uid CrtM^k. During 

 the next few days they licranu' vry aluuKhmt iud.vd. so that on 

 one occasion 230 of th(nii wow^ jiickt'd up in less tluin an liour's 

 collecting. On Jan. VI 1 l)f<;aii to iind euiz' masses attached to 

 certain sponges, matted al-:;e. luauiirove imoIs. and sundry moor- 

 ing stakes in the "creek." I had not ht^t'ove found any in this 

 place, as stated above. The imdihi'a m-hs were obsei-ved in copu- 



tachment of the eirir-nuissfs \va> nio>r t're(juently rr. some firm 

 object. AVitliin thr w.M-k -Ian. 10 17 tle^y l.-au to di^app^'ar. and 



obtainable in the creek.'' Tiiis oecurrenee seems to form a good 



