1894.} The Classification of the Arthropoda, 129 
of the shell gland of the Entomostraca often made comparisons 
between it and the “segmental organs” of the Annelids, but 
the trouble was that the former terminated blindly internally, 
while in the Annelids the organ formed a tube connecting the 
body cavity (ccelom) with the interior. The problem was 
solved by Sedgwick (’88), who showed that in Peripatus the 
nephridia were closed internally, but that they were still ne- 
phridia as proved by development, and that we have here to 
deal with a greatly diminished celom. In the light of these 
facts it is now placed beyond a doubt that in the antennal and 
shell glands of the Crustacea, and in the coxal glands of Arach- 
nids and Limulus, we have true nephridia.’ In all there is 
the formation of a ccelom, a division of the cœlom of certain 
somites into dorsal and ventral moieties, and a development of 
the lower portion irto end sac and nephridial tube, the latter 
portion breaking through to the exterior.’ 
Following the discoveries by Sedgwick that the genital 
ducts of Peripatus were modified nephridia, came the observa- 
tions of Heymons (90), Cholodkowsky (91) and Wheeler (’93), 
all of which show that exactly the same conditions exist in the 
Hexapods, while Laurie (90) has demonstrated that it is at 
least probable that the same holds true for the Scorpions. I 
made no observations on the origin of the genital ducts of 
Limulus, and I do not recall any account of their development 
in the Crustacea. In the latter group, however, there is not a 
little evidence of an anatomical character which is easiest in- 
terpreted upon the same hyp&thesis. There these ducts are met- 
americ, and may occur in different somites in the different 
sexes. This condition is to be explained in two ways, as has 
Previously been pointed out by Lankester. Either the ducts 
are to be regarded as new formations, or they are previously 
existing structures modified for reproductive functions exclu- 
sively. That this latter is the case, and that the ducts are 
cag is rendered probable by the following considera- 
*These drgans have been shown beyond a doubt to be mesodermal by Grobben 
(79), nein (’89, '90 and ’93), Kishenouyi (91), Lebedinsky (92), Laurie ('90), 
stc., and yet Bernard (93), with these facts available, bas recently attempted to de- 
tive these structures from the glands of annelidg—ectodermal Pon g 
the facts presented by those who have actually investigated the subject. 
9 
