1914] Esterly: Ctenopliora of the San Diego Region 35 



It can only be said that if vertical migrations take place, there is 

 no evidence to that effect in our data. Pleurohrachia was obtained 

 with the closing nets in 29 hauls. It was not taken below 50 fathoms : 

 each of fonr hauls from 50 to 40 fathoms with the Nansen net con- 

 tained one animal ; five were taken in one haul at 30-25 fathoms, two 

 in two hauls at 20-15, four in three hauls at 10-5, and 22 in three 

 hauls between five fathoms and the surface. The Kofoid net obtained 

 Pleurohrachia in ten hauls between 4 and 15 fathoms, there being 38 

 specimens in all, 15 of them in one haul at nine fathoms. It seems 

 surprising that there were not more successful hauls in such a large 

 number with the closing nets. As it is, there is nothing to show where 

 the animals are during the time when they are absent from the surface. 



These results are interesting in view of certain statements of Mayer 

 (1912). He says (p. 12) that the ctenophores sink far into the depths 

 during storms, and that the surface must have been very smooth for 

 hours before the organisms move upwards from their ' ' deep retreat. ' ' 

 Such observations may show why Pleurohrachia is taken in such a 

 small proportion of surface hauls, but they increase the expectation 

 that closing hauls ought to be more successful than in our experience. 



We are in position to speak on the basis of a few hauls only with 

 regard to the manner of occurrence of the other ctenophores, so that 

 it is uncertain what their behavior really is. Some points, however, are 

 of interest. 



Euplokamis {Horniiphora) was obtained in 17 hauls, 15 of which 

 were made in the summer. During July, 63 animals were taken in 

 four hauls ; during June there were nine in nine hauls, and one in 

 both August and September. July, therefore, is as pre-eminently a 

 favorable season for Euplokamis as August is, in comparison, for 

 Pleurohrachia. Furthermore, considering the summer season as a 

 whole, all the hauls from 10 p.m. to 2 a.m. (3 in number) were suc- 

 cessful and contained 49 of the 74 animals. Specimens did not ap- 

 pear in any of the hauls between 8 a.m. and 6 p.m. The time of the 

 plurimum of Euplokamis at the surface is during the period when 

 Pleurohrachia is rare or absent, so there is a suggestion that the two 

 organisms are distinguished by their behavior as well as by their 

 structure. This point has been developed at greater length in con- 

 nection with studies from the Institution on the Chaetognatha 

 (Michael, 1911) and the Copepoda (Esterly, 1912). Its apparent 

 recurrence here is, consequently, worth noting. 



