SEA-FISHERIES LABORATORY. "263 



tlie year the numbers are under 10 at a time, generally 

 one or two only. 



From the records in the Blue-book (Cd. 3837, pp. 233, 

 241) it seems that this oceanic form occurs com- 

 paratively rarely at Plymouth and elsewhere in the 

 English Channel — at Plymouth on three dates in 1904, 

 and on two only in 1905. Unfortunately no numbers are 

 given in the Blue-book, so no exact comparison can be 

 made ; but the probability is that — looking at our records 

 of frequent occurrence over six months and of hauls 

 extending up to 85 and 95 in a net — -the species is very 

 much more abundant in the Irish Sea than in the English 

 Channel— why, then, is the Irish Sea described as the more 

 " neritic " of the two? 



OlKOPLEURA. 



The common species of Oikopleura that occurs in our 

 district (0. dioica) is also a form which deserves special 

 notice. It occurs throughout the year, being present in 

 every month, and represented in nearly every gathering. 

 It is absent or rare in the case of the hauls taken on a 

 few dates between August 24th and 28th, and then again 

 on September 4th and 5th. With those exceptions, 

 Oikopleura is one of the most constant of organisms at 

 all times of the year, and, moreover, is usually present in 

 quantities that range within narrow limits, so that it does 

 not vary, to the extent that some Copepoda and Diatoms 

 do. In the winter months — December, January, February 

 and March — the numbers taken are low, but from April 

 to Xovember inclusive quantities of a thousand or two 

 per net are very frequently taken. The highest numbers 

 occur in April, and they only reach 5,500 per net, so 

 there is no marked maximum. 



In some cases the numbers of Oikopleura remain 



