BOS 



CRUSTACEA. 



Family CAPRELLID^E. 



In the study of the Caprellidae, the sexual differences are found to 

 be great and perplexing, and even in the same sex there are wide 

 variations of form in a single species. These differences are most 

 strikingly exhibited in the relative lengths of the head and first tho- 

 racic segments, the character of the hands of the second pair, the 

 position of the second pair of legs on the segment bearing it, and also, 

 to some extent, in the relative lengths of the pairs of antennae, and 

 the several thoracic segments. Besides these differences, there is the 

 existence of ovarian plates in females, beneath the third and fourth 

 segments of the thorax, which are wanting in males. 



In a single species, the males may have the head three or four 

 times shorter than the first thoracic segment; while in the females it 

 is but twice as large. Again, in other males of the same species, the 

 proportion may be nearly that of the female. 



In males, the second pair of legs is often attached to some part of 

 the posterior half of the second thoracic segment; in females, the 

 attachment is always anterior to the middle of this segment, and 

 often quite to the anterior extremity. But, while there is the widest 

 diversity in this respect between the males and females of the true 

 Caprellse, the difference is slight, or none, in Proto and Protella, 

 the attachment being in neither sex posterior to the middle, and often 

 much anterior. 



The hand of the second pair in male Caprellse of some species, has 

 often two prominent teeth anterior to the middle of the palm, one of 

 the two (the more apical) sometimes truncate and rhombic, and the 

 palm is frequently a little concave ; besides these teeth, there may be 

 another on the same margin, exterior to where the end of the finger 

 shuts down. But this arrangement does not occur in all males, nor is 

 it absent from all females, unless it be that the truncate rhombic 

 form of tooth is a male characteristic, whenever it occurs, as we deem 

 probable. In females, the teeth on the palm are usually less promi- 

 nent, and the palm itself is more frequently somewhat convex. 



The second, third, fourth, and fifth segments of the body in Ca- 

 prellse are commonly approximately equal in length. In the more 



