NO. 1783. NORTH AMERICAN LERNMOPODIDM— WILSON. 191 



Here the development of the Lernseopodidse rested for nearly 

 thirty years until Claus in 1862 filled in one of the missing stages in 

 the life history of AcJitheres ])ercarum. But Claus himself stated that 

 he was unable to finish his investigations, and many gaps were still 

 left in our knowledge of this crustacean family. 



In 1870 Edouard Van Beneden gave as the fourth paper in his 

 researches on the embryogeny of the Crustacea what might be called 

 a mosaic development of the Lernseopodidse. 



His series of stages, which began with the segmentation of the egg 

 and closed with this same first copepodid larva, were selected from 

 the genera Ancliorella, Lernxoyoda, Brachiella, and Hessia"- 



Olsson in 1877 published the figure of a larva of AcJitheres perca- 

 rum, but gave an extremely meager description, while the figure 

 itself was so small as to show no details. 



Finally Vejdovsky in the same year (1877) worked over again the 

 anatomy and development of Tracheliastes yolycolpus, but like Nord- 

 mann and Kollar he followed the metamorphosis only to the first 

 copepodid stage. His description and figures of the development 

 inside the egg, however, are the most complete and the best that 

 have ever been published. 



These five papers (beside Olsson's single figure) comprise practi- 

 cally all that has appeared upon the development of this family, the 

 Lernseopodidse, up to the present time. 



The reason why so many of them stop with the first copepodid 

 larva is readily understood when it is recalled that this is the only 

 free swimming stage, and is therefore the one during which the larva 

 seeks out its host. Even Claus, who is the only one to describe any 

 of the subsequent stages, was forced to be content with female 

 larvae 2 mm. long (really adults) and a male larva that was prac- 

 tically fully developed. But he described both of these in consider- 

 able detail and thus furnished an important contribution to their 

 life history. 



Claus gave it as theoretically probable that this first copepodid 

 stage, at which all the accounts stop, passed at the next molt into 

 an attached form in which the number of body segments and appen- 

 dages was not increased, but the frontal filament was put into oper- 

 ation for attachment to the host, the mandibles were inclosed in the 

 proboscis, and the setae of the swimming legs and the furca were de- 

 generated from lack of use. He was not able to find such a form, but 

 it has been discovered in connection with the present work, and 

 while it does not conform in all details to what he prophesied, it 

 shows a remarkably accurate conception on his part of its general 

 features. But his actual obsei^ations were made upon larvae and 



oThis was a new genus named for the first and as it has proved the last time, but 

 not described or figured, except in one or two embryonal stages. 



