NO. 1504. 



AMERICAN PARASITIC COPEPODS— WILSON. 



691 



the abdomen. This is similar to the condition found in the chalimus of 

 the Calig-inffi. 



The lirst thorax .segment is stiJl imperceptibl}- fused with the cara- 

 pace, but the second and third segments are clearly separated f i-om it, 

 though the}' have become partially fused i?iter se. 



The second segment has become nearly as wide as the carapace and 

 its lateral margins extend out over 

 the bases of the second legs in the 

 form of broad lobes. The third 

 segment is also widened and now 

 bears a pair of swimming legs 

 similar to the first two pairs. The 

 fourth and g-enital segments still 

 remain fused with the abdomen, 

 but have elongated considerabh', 

 while the constriction which indi- 

 cates the future separation of the 

 fourth segment is more clearly 

 marked. 



The anal lamina? are longer 

 than in the metanauplius and 

 closer together, but the plumose 

 setas with which the}" are armed 

 are greatly reduced in size, and 

 there are only three of them on 

 each lamina, all terminal. The 

 other plumose seta? of the meta- 

 nauplius are here represented by 

 two small spines on the outer 

 margin of each lamina. 



On comparing this chalimus 

 with that of the Caliginse we 

 again lind evidence of precocious 

 development, this time in the sep- 

 aration of the fourth segment. 

 The second and third segments 

 are fused i7iter se in both subfam- 

 ilies; in the Caliginae there is no 



0-5 mm 



-The (female) chalimus of Alebion 



GLABKR. 



indication of the separation of 



the fourth segment, while here that separation is clearly indicated 

 by a well-marked constriction. This would mean very little by 

 itself, but at the next molt, when the fourth segment is full}' sepa- 

 rated in both subfamilies, we find it without appendages in the Cali- 

 giage but with a pair in the Euryphorinee. 



