196 bulletin: museum of compaeative zoology. 



origin of the nephridia of Annelids, the most that can be said is, that 

 the endsac of the antennal gland in Crustacea may be homologous with 

 the nephrostome of the nephridium in Annelids, together with perhaps a 

 part or all of the nephridium peripheral to the base of the nephrostome. 



In some points there is considerable difference between the nephro- 

 stomic end of a nephridium in an Annelid and the endsac of an antennal 

 gland in Macrura. The lumen of the former is usually in direct contin- 

 uity with the coelom, and is ciliated ; the latter is closed and non-ciliated. 

 After the work of Grobben ('79) on the shell gland, this question occa- 

 sioned considerable discussion, and it was claimed that these differences 

 must invalidate any proposed homology between the two organs ; but 

 later investigation has shown that the blood sinuses surrounding the 

 endsac of the antennal gland are not homologous with the nephrostomic 

 spaces in Annelids, and therefore the premise upon which this discussion 

 was based is destroyed. 



Eisig ('87) holds that the nephridium of Annelids has two functions : 

 (1) the elimination of solid particles from the coelomic spaces, a duty 

 performed by the nephrostome and in which the cilia take an active 

 part; and (2) the excretion of soluble products from the blood and 

 coelomic fluid, a function exercised by the excretory cells. If this view 

 be correct, — and there are many things which support it, — the neph- 

 rostomic function is not directly represented in the autennal gland of 

 Crustacea, and we therefore cannot, expect close morphological resem- 

 blance. Hence it seems probable that the closed endsac, in place of an 

 open nephrostome, does not necessarily invalidate a general homology 

 between the two sets of organs. 



B. The Number of Metameric Organs of this Nature in Crustacea. 



Thus far I have considered the glands in Crustacea from one segment 

 only, — that of the second antenna. In Annelids the nephridia are re- 

 peated through a relatively large, although varying, number of segments. 

 Is such metameric repetition realized in Crustacea ? 



Boutchinsky ('95, p. 170, Tab. VI. Fig. 145, Tab. VII. Figs. 157, 162) 

 has described in the first maxilla of Gebia the development of a meso- 

 dermic structure which takes on the form of a tubule closely resembling 

 the antennal gland in histological detail, inclusive of staining qualities. 

 Only the earlier stages of this organ are described, but from this evi- 

 dence the author thinks the organ is probably excretory, and that it 

 belongs to the same series as the antennal gland. 



