552 proceedings of the National museum. vol. xxvni. 



The other mouth parts and the four pairs of swimming- legs develop 

 steadily toward the adult form, with no marked changes at any one 

 moult. The only features worthy of note are in the development of 

 the first and fourth pairs of swimming legs. 



In early stages the first pair (fig. 50, 1) have a well-defined endopod, 

 much smaller than the exopod to be sure, and consisting of but a 

 single joint terminating in two small seta?. Later this rudimentary 

 endopod almost entirely disappears, its place in the adult being indicated 

 by a long, slender seta. 



The fourth legs are made up at first of two short and very broad 

 disk-like segments, totalty unlike the long and slender adult form (4). 

 Furthermore, there are no setse anywhere upon them except at the tip 

 of the terminal joint where four very short and stubby ones stand in 

 a row. With almost the first chalimus moult, however, the nature of 

 these legs changes radically, and they quickly narrow and elongate, at 

 the same time acquiring setse upon all the joints. 



With the beginning of the chalimus period the digestive organs 

 change into the adult form, and the reproductive organs appear. The 

 latter grow rapidly in the male and have attained their full develop- 

 ment by the close of the chalimus period, but in the female they 

 remain rudimentary until fertilization, which takes place onty after 

 the larva? have become free swimming. The genital segment in the 

 female remains small, deeply lobed posteriorly, and with the fifth legs 

 showing prominently for quite a long time after the close of the 

 chalimus period. 



The nervous system starts in a large ganglion just beneath the dorsal 

 surface of the carapace, posterior to the eyes. This ganglion is ellipti- 

 cal in shape, the eyes being situated just above its anterior end. A 

 pair of nerves, corresponding to the first pair in the adult, extend from 

 the anterior end of this ganglion to the eyes. From the posterior end 

 in early chalimus stages two or three pairs of slender nerves extend a 

 short distance backward but do not reach beyond the carapace. This 

 one ganglion evidently corresponds to parts of both the supra- and 

 infra-oesophageal ganglia in later development. As the young cope- 

 pod grows by successive mountings, and the various appendages appear 

 in regular order, the nervous system also develops. In this way for 

 each of the appendages there appears at the proper time the pair of 

 nerves which are to innervate their muscles until the whole system is 

 completed. After a study of these forms extending over several years 

 it may be stated with a fair degree of accuracy that this period of 

 attachment to the host lasts from four to six weeks. During that time, 

 to judge from the material collected, there are at least five moults, if 

 not more. 



At the close of the period the appendages have become fully 

 developed, and with the last moult the filament separates just at (lie 



