NO. 1783. NORTH AMERICAN LERNJEOPODID/E— WILSON. 221 



pulled, and backward on the opposite side. This motion is then 

 reversed when the intestine is pulled to the opposite side. These 

 movements become stronger with the maturing of the larva, and in 

 the adult they produce a complete circulation. 



There are no blood vessels nor any heart. What Claus describes 

 as a pulsating organ ("pulsirende Organ") occupies exactly the 

 position of the median maxillipedal gland, already described. The 

 body is strongly narrowed just posterior to this point and the lumen 

 of the body cavity is tightly filled by the median maxillipedal gland, 

 the lateral glands, the ovaries or testes, and the enlarged anterior end 

 of the stomach. Naturally the blood streams through the narrow 

 interstices between these organs with considerable force and often 

 moves the dorsal portion of the organs with every sway of the diges- 

 tive tract. When seen through the outer body wall this gives the 

 impression of a pulsating organ, but nothing of the sort can be 

 found in the larva. 



SUBSEQUENT STAGES. 



At the next molt both sexes become mature — that is, they are 

 adults, and although they increase afterwards in size, especially the 

 female, there is no further change in bodily structure or the append- 

 ages (figs. 38 to 43). One thing, however, is still left to be accounted 

 for, and that is the coming together of the sexes. At present we have 

 them each attached by a filament to the host, whereas we know that 

 in the matured adults the pigmy male clings with his maxillipeds 

 to the body of the female. How is this transfer accomplished by a 

 creature that can not swim ? 



From this' second copepodid stage there is a steady increase in the 

 difference in size between the sexes. The female grows faster than 

 the male, particularly the posterior portion of the body, and the 

 second maxillse elongate until they are often as long as the entire 

 body. The attachment filament at the same time shortens until all 

 that is left of it is the slender stalk between the attachment disk and 

 the tips of the maxillae. 



In the male the head and body remain approximately the same 

 size; the second maxillae do not elongate nor does the attachment 

 filament shorten. The claws at the tips of these maxillae are retained, 

 as are also the muscles comiected with them. Indeed, since the fila- 

 ment in this sex does not become fused with the maxillae, the only 

 way in which the male retains hold of it is by means of the claws 

 driven into its swollen proximal end. The purposes of these differ- 

 ences is now manifest, for they enable us to understand how the 

 union of the sexes takes place. 



The females were permanently attached to their host in the first 

 copepodid stage and can not afterward be changed. On the contrary 

 the little motion at first allowed by the long attachment filament 



