44 



In most cases it has already been plain the larval passes 

 without break into the adult condition. This feature is parti- 

 cularly evident in the Entomostraca, which remaining small 

 preserve many larval features. Even the Cirripedia may be 

 looked upon as large babies. 



As conditions are at present, I must content myseK with 

 referring to one example. Dr. Marie Lebour has recently described 

 the early history of Calanus finmarchicus from the stages pre- 

 pared by IVIi'. Crawshay at Plymouth, and she has been good 

 enough to send me the following measurements : — 



Xauplius Stages. Copepod Stages, 



123456789 10 11 12 



0-21 0-27 0-42 0-48 Ool [0-67] 0-8 1-2 1-5 1-8 2-3 [29] 



At the tweKth stage the young Calanus is fully developed, 

 all the limbs being completely formed. One or two more ecdj-ses 

 appear to be necessary before the adult size is attained. The 

 larval stages were found to be passed through m about two months. 



If the development was equally rapid all the year a maximum 

 of six broods could be said to be produced. But we know from 

 the results of plankton investigations that this species and Cope- 

 poda generally increase enormously in numbers in summer, and 

 the increase of the young and the nauplii is particularly noticeable 

 about May and June, and agam is observed about September. 

 Reproduction then undergoes a special intensity in spring and 

 autumn, and this periodicity appears to be referable to the period 

 of growth in the summer, and points to a diminution both in 

 reproduction and growth in the winter. 



It must not be forgotten, however, that this and the other 

 pelagic Copepod a are holoplanktonic, and that the double wave 

 of Copepoda observed in the Irish Sea, at Plymouth and at Cuiler- 

 coats is a general one affecting the whole of the North Atlantic. 

 It is the inshore manifestation of a change which is oceanic in 

 its scope. Gran sees reason for believmg that this species at least 

 only reproduces once a year, that there is an annual spawning 

 season, but the facts appear to pomt to the event happening at 

 least twice, the amiual phase being a short summer followed by a 

 long winter generation. In tropical waters the generations are 

 probably still more frequent, and it is from the tropical Atlantic 

 that the North Atlantic obtains its annual supplies. 



