242 KINGSLEY. [Vol. VIII. 



of the somites of the Arthropods, still if the metastoma be ad- 

 mitted as an appendage in the Crustacea, the correspondence 

 between the opening of the duct of their shell gland and that 

 of the coxal gland is exact. Another fact which goes to show 

 that the shell gland is ncphridial is, that it and the antennae 

 gland but rarely coexist in the same individual (Nebalia, Claus). 



From the evidence presented by the nephridia therefore, we 

 are justified in the close association of the Arachnids and the 

 Xiphosures, We are also apparently led to associate these two 

 groups more closely with the Crustacea than with the Hex- 

 apod s. 



The correspondence between the genital ducts of Limulus 

 and those of the Scorpion is as close as that of the respira- 

 tory organs. In Limulus the genital ducts in both sexes open 

 upon the posterior surface of appendage VII. In the scorpions 

 Narayanan ('89) has shown that the genital operculum is a 

 paired organ in both sexes and that the genital ducts open 

 up on what is morphologically its posterior surface. Farther, 

 Laurie's observations upon the development of the ducts show 

 beyond a question that they belong to somite VII. In Limu- 

 lus I have failed to see the development of the duct, it being 

 apparently delayed even longer than in the scorpion. 



There is to-day little doubt that the genital ducts of all 

 Arthropods are to be regarded as modified nephridia. I have 

 alluded, just above to the method of development of these 

 structures in the Hexapods and in Peripatus. In the scorpion 

 Laurie's account of their development would indicate that here, 

 too, they are to be classed in the same category, the later 

 appearance of their external opening being the greatest objec- 

 tion to such a view. 



In the Crustacea we have, so far as I am aware, no 

 direct observations upon the ontogeny of the ducts, but the 

 facts of comparative anatomy are all but conclusive. Thus the 

 relations of the gonads to the persistent coelom are such as 

 would be required were the ducts segmental organs, while the 

 varying position of the ducts themselves in the two sexes of 

 the same species and the fact that in abnormal instances two 

 pairs of ducts may occur in the same individual, show that they 



