32 THE DEVELOPMENT OP 



out the egg, or aggregated at one pole of the ovum. In the 

 Crustacea and other Arthropods, as I have already shown 

 ('866, pp. 103, 112 to 138) and contrary to the usual charac- 

 terization, the yolk is superficial and the protoplasm central, 

 just as we might expect it to be in an egg, the mothers of 

 which had only recently acquired the capacity of provid- 

 ing the growing germ with an abundance of nourishment. 

 Then, too, the character of the segmentation, which as I have 

 also shown (L c.) is neither superficial nor centrolecithal, 

 but is regular and total, is like that of an alecithal egg, 

 and the food yolk has not long enough been present to 

 modify but slightly this regularity and totality. 



Now it is admitted by all that the Crustacea have de- 

 scended from the Annelids and from some member of that 

 group where there were a considerable number of seg- 

 ments. The persistence of several modified segmental or- 

 gans in the Crustacea, 1 indicating at least the inheritance 



1 The antennal glands, coxal glands, and so-called shell glands, are 

 clearly derivatives of the nephridia of Annelids, with which they agree 

 in position, function and to a certain extent in structure, if due allow- 

 ance be made for the almost total obliteration of the coelom and the 

 absence of cilia in the Arthropods. To this series, which represent 

 the second and fifth segments of the body, I would here state my be- 

 lief must be added still others in both Crustacea and Arachnida. In 

 the decapods, for instance, the genital openings are paired and open 

 at the inner bases of the legs, but the position of that opeuing varies 

 in the two sexes ; being in the female at the base of the eleventh and 

 in the male of the thirteenth pairs of feet. This diversity in point of 

 opening of the genital glands in the two sexes of the same species is, 

 it seems to me, inexplicable upon any other ground than that the ovi- 

 ducts and vasa deferentia are themselves modifications of pre-existing 

 metameric organs, and the only organs in the annelids which would 

 answer the requirements of the case are the nephridia. This view is 

 rendered more probable from the fact that in many annelids the ne- 

 phridia are at once organs for carrying off nitrogenous waste and gen- 

 erative products as well, while in others (e. g., Lumbricidse) certain 

 of these organs become modified for carrying off the male and others 

 the female reproductive elements. In this connection, too, it is to be 

 noticed, thaf. while I have made no observations on the development 

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