396 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



11,000 on November 7th. Lamellibranch larvae are even 

 more abundant than Gastropods (nearly 18,000 on 

 January 4th). Some hauls reach the thousands in each 

 month of the year, and some of the chief hauls are as 

 follows :— 22,000 on May 20th, 16,000 on June 20th, over 

 41,000 on September 7th, 56,000 on October 7th, and 

 12,000 on November 7th. It is evident that several of 

 these groups of larvae, in addition to a maximum early 

 in the year, have a second climax in the late autumn. 



Medusae and Ctenophora. 



The Medusae are present in Port Erin Bay through- 

 out the year. The numbers are low (only a few 

 individuals in each haul) in January and February, then 

 increase gradually to the maximum of 615 on May 20th, 

 fall again in summer, rise to a second maximum at the 

 end of September and beginning of October (380 on 

 September 23rd; 406 on October 7th), and are again low 

 till the end of the year. 



Much work has still to be done in determining in 

 detail the specific forms present at different times. 

 Probably those of the May and September maxima belong 

 to different sets. 



Pleurobrachia, our commonest Ctenophore, occurs in 

 nearly every month in the year, but especially in 

 autumn (end of September and October), when it may 

 add considerably to the bulk of the plankton, and be of 

 real importance, not as a food-matter, but as an enemy 

 or a competitor injuring forms more useful to man. 



Our knowledge of the extent to which some animals 

 in the sea prey upon others is still very incomplete and 

 inexact. We have been constantly on the watch during 

 these plankton investigations for any cases that would 

 add to knowledge on this matter, but it is surprisingly 



