NO. 2063. KORTH AMERICAN PARASITIC COPEPODS— WILSON. 



585 



and fifth segments. The anterior pair (a, fig. 6) are short and C3din- 

 drical and each originates in the groove separatmg the second and 

 thii-d thorax segments on the dorsal surface about half way from the 

 lateral margin to the midlme. It then runs diagonally inward and 

 backward and is mserted in the side of the digestive tube, a little 

 above the center. 



The median pair (m) are strongly flattened doreo-ventrally; each 

 originates at the center of the lateral margin of the fourth segment, 

 extends directly mward, and is inserted in the wall of the stomach; it 

 is narrow at its origm but \videns out greatly at its insertion. The 

 posterior pair (2^) are cylindrical again; each originates on the dorsal 



Fig. 7.— The male of Clavellisa cordata. an' and an", Antennal muscles; md, mandible 

 muscle; mi' and mx", MAxttLAEY muscles; mxp, muscles of the maxilliped. 



wall of the genital segment, extends diagonally forward and inward, 

 fuses with its fellow from the opposite side, and is inserted in the cen- 

 ter of the dorsal wall of the intestine. The anterior and posterior 

 pairs pall the digestive tube backward and forward, while the median 

 pair pull it to the right or left. 



Another pair of special muscles may be called the cjaculatory 

 muscles; they are situated on the dorsal surface of the semen recep- 

 tacle in the genital segment (em, fig. 8). Each extends from the 

 thickened margin of the external opening of the oviduct diagonally 

 inward and backward to the center of the dorsal surface of the sperm 

 receptacle. A contraction of these muscles aids in forcing the eggs 

 out into the external sacks, and may at the same time help to dis- 

 charge the contents of the sperm receptacle. 



6. The musculature of the male. — In those males in which the 

 cephalothorax and trunk are either in the same line (Achtheres, etc.) 

 or somewhat flexed without any fusion (Brachiella, etc.) the general 



