554 I'ROCEEDINaS OF THE NATIONAL MUSEUM. vol. xxviii. 



iiiundiblcs, a mouth tube or prolKK-is, iirst and second niaxillipeds, and 

 three pairs of rudimentary swimming legs. 



8. 'Pile tliird moult occurs at al)out the same interval as the others. 

 The first thoracic segment has t)ecn entirely, and the second partially, 

 fused with the head. The third segment has elongated and the rudi- 

 ments of the fourth thoracic legs appear upon its posterior ventral 

 surface. The genital segment still remains fused with the abdomen, 

 but the two have increased considerably in size. The first antennie 

 have become three-jointed; the other ai)pendages remain unchanged," 

 save that the swinuuing legs advance toward the adult form. 



9. The larva now seeks its host and moults again into what is known 

 as the chalimus stage, the chief characteristic of which is the devel- 

 opment of a long cord or filament by means of which the young are 

 attached to their host. This tihinnmt is made out of the material 

 secreted ])y a median gland situated just in front of the eyes. 



10. The changes which take place during tliis fourth moult and 

 those which subsequently occur in the several moults of the chalinuis 

 period ai"e in the line of gradual development toward the adult form. 

 The carapace, at first squarely truncate posteriorly, gradually develops 

 a lobe on either side and widens. The first three thoracic segments 

 fuse with the cephalon, and the sutures on the dorsal surface of this 

 ccphalo-thorax appear and become well developed. The genital seg- 

 ment and the abdomen separate at the second chalinuis moult, the 

 abdomen at first being several times the larger. The eyes move 

 steadily forward with each moult, l»ut as the appendages on the 

 ventral surface move forward also the relation of the two remains 

 unchanged. 



11. The only appendages worth noting are the tirst and fourth 

 swinmiing legs. In the early chalinuis stages the tirst pair have a 

 well-detined endopod, consisting of a single joint tei'minating in two 

 small setfe. Later this disappears and its place in the adult is indicated, 

 if at all, by a long seta. The fourth legs are made up at first of two 

 short and broad, disk-like segments, without seta? or spines. With 

 successive moults they narrow and elongate into the adult form, and 

 acquire l)oth spin(\s and setce. 



12. This attached stage lasts from four to six weeks, and the larva 

 moults at least five times. At the close of the stage the male is prac- 

 tically fully developed, but the female remains inunature, so far as the 

 reproductive organs arc^ concerned, until fertilization has been efl'ected 

 and the ova begin to descend the oviducts. With the last chalimus 

 moult the connecting filament separates just at the frontal margin of 

 the carapace and the copepod enters upon its free adult existence. 



