568 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.55. 



ARTIFICIAL KEY TO THE SPiiCIES. 



Cephalothorax (hammer) only half wider than long and smooth; neck without 

 processes, longer than the rest of the body combined ; genital segment longer 

 than wide lumpi (Kr0yer), 1837, p. 570. 



Cephalothorax (hammer) two or three times as wide as long and covered with 

 soft processes, often branched ; neck shorter than genital segment ; the latter 

 wider than long laevigatum Guerln-Menevillo, 1839, p. 575. 



Remarks. — From the series of developmental stages here presented 

 it can be easily seen that the body dimensions will vary greatly with 

 the growth. The hammer tends to become more and more elongated 

 transversely; its surface remains smooth and unbroken in lumpi, 

 while in taevigaturm it becomes broken into numerous processes and 

 warts. Once this latter sort of growth is begun it is manifest that 

 there will be no limit either in the number or the pattern of the ex- 

 crescences. The antennae and mouth parts alone will show any regu- 

 larity of position, size, or shape. 



Furthermore the same individual will show a very different pat- 

 tern of cephalothorax at different stages in its growth. And prob- 

 ably no two individuals of the same species will ever be just alike. 



The neck varies greatly in length, in actual diameter, and in rela- 

 tive diameter at its anterior and posterior ends. In general, the 

 older and the larger the parasite becomes, the smaller is the neck 

 diameter in comparison with the other body regions. The trunk 

 changes the least of any part of the body, but even it must become 

 considerably swollen with the maturation of the eggs and shrunken 

 after their extrusion into the external sacks. On the other hand, 

 there is the greatest chance for variation in the posterior processes. 

 They start as simple branches at the point of fusion of the anal 

 laminae with the genital segment, and become more and more com- 

 plexly branched with growth. As in shrubs and trees, therefore, 

 we must not expect to find exact duplicates of any particular pattern, 

 but only a general similarity in the mode of branching. 



In the same way we might well find the tips of the branches swollen 

 into spheres in one specimen, normally cylindrical in another, and 

 flattened in a third. Such considerations as these make any dif- 

 ferentiation of species upon the external characters of the female 

 alone very questionable. The best, and probably the only reliable, 

 method of separating species will be by comparison of the males and 

 young females whose mouth parts have not yet become degenerate. 



Seven species of the genus have been thus far proposed, but a care- 

 ful comparison of the descriptions given, which are based entirely 

 upon the external appearance of the female, apparently reduces the 

 species to the two given above. Since most of the descriptions place 



