IO2 THURLOW C. NELSON. 



which, so far as my knowledge goes, has not hitherto been 

 stressed. The presence of nannoplankton and of organic debris 

 within the ctenophores demonstrates that these animals make 

 use of their ciliated canals for the transport of minute forms in 

 much the same manner as does a bivalve mollusc. The pos- 

 session of this feeding mechanism makes available to them the 

 nannoplankton which is by far the greatest constituent of the 

 total plankton, a constituent, moreover, which may be mainly 

 unavailable to their larger ccelenterate allies. This may explain, 

 in part, how such vast hordes of ctenophores can exist together 

 for long periods of time (cf. Nelson, '22). 



Table II. contains a summary of the food organisms found in 

 Mnemiopsis during July. 



To summarize the data in Table II.: of 65 Mnemiopsis 

 examined during July, 75 per cent, had eaten bivalve larvae, 

 50 per cent, contained Crustacea, 15 per cent, held gastropod 

 larvae, while 6 per cent, contained detritus and nannoplankton. 

 One specimen about 3 cm. long had eaten 126 early oyster 

 larvae. 



On December 21, of 10 specimens examined 5 contained a total 

 of 26 large Calanus and I gastropod larva. Examination of the 

 ctenophores at this time and again on January 19, 1924, revealed 

 a most interesting fact regarding digestion in Mnemiopsis. 

 Copepods, as is well known, contain large oil globules, representing 

 stored nutriment. In every ctenophore examined during the 

 winter, oil globules derived from the copepods, were found to be 

 deposited in thick rows beneath the paddle plates. Many 

 minute oil globules were seen passing out of the anus, and one 

 specimen was observed in the act of casting out through the 

 mouth a thick rope of oil globules and detritus. Apparently but 

 little of the oil obtained from the crustaceans used as food is 

 metabolized by the ctenophores, at least at low temperatures. 

 The storage of the oil in such large quantities beneath the paddle 

 plates may serve an important function in decreasing the specific 

 gravity of the body. This accumulation of oil at a time when 

 also the density and the viscosity of the water are greatly in- 

 creased through low temperature, renders the animal capable of 

 suspension in the water with a minimum of activity of the paddle 



