220 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.39. 



The testes begin in the same manner as the ovaries, the separate 

 masses becoming afterwards the lobes of the fully devoloped organs 

 (fig. 35). The deferent duct (vd.) at first turns forward to the ventral 

 surface, then swings back to the dorsal surface, runs diagonally to 

 about the center of the lateral surface, where it is greatly swollen, 

 and finally turns diagonally forward again to the opening on the 

 ventral surface of the genital segment. The free portion (fd.) of the 

 duct is much larger than the oviduct, chiefly owing to the increased 

 thickness of its wails. In the swollen anterior convolutions of the 

 duct may be distinctly seen the cells which are to be transformed 

 later into spermatozoa. 



As development proceeds the deferent duct, like the oviduct, 

 becomes more and more convoluted and swollen, until it finally fills 

 the entire cavity on either side of the digestive tract, and it presses 

 against the latter so much that the rectal portion of the intestine 

 becomes flattened laterally into a mere slit, difficult to distinguish 

 except in transverse sections. In this second copepodid larva the 

 entire posterior segment of the body, which is a fusion of the two 

 posterior thoracic segments and the abdomen, is filled in the male 

 with a mass of ceils (k, fig. 32) containing fine granules (Clans' s 

 "Kornchenhaufen"). These become joined later with the posterior 

 portion of the deferent ducts and supply the cement substance which 

 forms the outer covering of the spermatophores. In this manner 

 practically the entire body cavity behind the cephalon is occupied 

 by the sex organs and the various accessories connected with them. 



CIRCULATORY SYSTEM. 



There are no real circulatory organs in this larva or in the adult. 

 The blood moves about freely through the large open spaces in the 

 body cavity, and is driven back and forth by the movements of the 

 digestive tract. Both the stomach and intestine have muscular 

 walls capable of strong peristaltic movements which show much diver- 

 sity. At one time they sweep forward, at another backward, and 

 again they start at either end and work toward the center, or they 

 may begin at the latter point and move backward and forward 

 simultaneously. These movements carry along with them the blood 

 which lies in contact with the walls of the digestive tract. But the 

 real movement is accomplished in a much more effective manner. 

 To either side of the digestive tract in the third thoracic segment is 

 attached a bundle of muscle fibers which run directly outward and 

 are fastened to the lateral body waU. These contract rhythmically 

 to the right and to the left, pulling the intestine quite a distance 

 away from the midline to the one side and then to the other. The 

 blood, following these lateral movements of the intestine, streams 

 precipitately forward on the side toward which the intestine is 



