NO. 1783. -NORTH AMERICAN LERN.EOPODIDM— WILSON. 



193 



while a union of the sexes takes pLace. The male develops no farther 

 but the female seeks a second host and on it undergoes a new degen- 

 eration, even greater than the first. 



V. Those in which the first copepodid stage alone is free-swimming; 

 all the larval development previous to this is passed inside the ego-, 

 while subsequent to it the copepod is a fixed parasite, usually showing 

 degeneration. 



CROUP 



DEVELOPMENT STAGES 



PERCENTAGES 



NAUPLIUS 



3 



/^ETA 



NAUPUU5 



I 



3 



COPEPODID 



2 



3 



ADULT 



3 





/ 



n 



m 



IV 



V 



^2 



so 



7S 



66 



SO 



16 



3 



u 



33 



SO 



^2 



^2 



Table showing comparative time spent in the egg (horizontal lines), as free swimmers 

 (black), and as parasites (squares), by the developing lakv^ of typical genera from each 

 of the five groups mentioned. 



Here belong the Choniostomatidae and the Lernaeopodid^. In the 

 latter family, according to Claus and others, some species hatch in an 

 advanced metanauplius stage, all ready for the molt into the first 

 copepodid stage. This molt consequently takes place in a remark- 

 ably short time, from ten minutes to an hour. In other species, as 

 observed by Kellicott and the present author, the larv« hatch directly 

 into the first copepodid stage and seek a host at once. 



The details of this extraordinary shortening of the free larval 

 period have never been brought out clearly, and that is the aim of the 

 following account. 



Proc.N.M. vol.39— 10 15 



