NO. 2194. NORTH AMERICAN PARASITIC COPEPODS— WILSON. 27 



declared. There are always two of them, no matter what the num- 

 ber of the horns may be, and sometimes they are not opposite the 

 base of the horns. Furthermore, they are present in the larva long 

 before the horns have started to grow. The stomach is lined with 

 a digestive epithelium of very irregular thickness, from which 

 scattering spherical cells project into the central cavity. These 

 contain the digestive fluids and also a large nucleus with distinct 

 nucleoli. 



The stomach passes insensibly into the intestine, which, in most 

 of the genera, is narrowed to a mere thread where it passes through 

 the neck and then widens again in the trunk. Sometimes (Ler- 

 naeoJophus) the intestine is convoluted in the lower portion of the 

 neck, but it is usually straight. In the trunk it lies nearer the 

 dorsal surface, between the ovaries and the oviduct, and is sometimes 

 flattened dorsoventrally (Sarcotretes), again laterally {Lernae- 

 olophus), or may even assume a three-cornered shape (Fennella 

 tridentata) , but is usually cylindrical. 



In species like Phrixocephalus tHangulus^ where the trunk is short 

 and wide, the intestine becomes baglike, and in the new genus C'olli- 

 praviis it is looped and folded back on itself, owing to the misplace- 

 ment of the neck. The intestine passes into the abdomen in those 

 genera {Lemaeolophus^ Pennella, etc.) which have a comparatively 

 large abdomen, and is bluntly rounded near the posterior end of the 

 latter. In the genera {Sarcotretes, Peniculus, etc.) with a small 

 abdomen it does not leave the trunk, but is bluntly rounded just in 

 front of the vulvae, and the rectum is given off from its upper pos- 

 terior corner. The re,ctum is very narrow and threadlike, and is 

 connected with the side walls of the abdomen by numerous muscles. 

 It is straight Avhen the abdomen is large, but in the other genera is 

 inclined dorsally. 



In every genus thus far examined there is an anal lamina on 

 either side of the external opening of the rectum, sometimes fair 

 sized and armed with setae, sometimes minute and destitute of setae. 

 But no matter how small the lamina may be there is an opening 

 through the body wall into its interior that shows its real nature 

 (fig. 57). 



The anterior end of the stomach is suspended from the dorsal wall 

 of the head by tAvo long and narrow muscles, and in the genus Ler- 

 naea there are additional sets of muscles on each of the lateral lobes. 

 The posterior end of the intestine is similarly connected with the 

 dorsal wall of the abdomen or trunk. The alternate contraction and 

 expansion of these muscles produce a forward and backward move- 

 ment of the entire digestive canal. This is most marked in the cope- 

 podid larvae, but persists to some extent in those adults whose bodies 

 are straight and not bent into a sigmoid loop. In addition to these 



