194 bulletin: museum of compaeatiye zoology. 



statement that the epidermis takes no part in the formation of the gland, 

 but concedes ('88, p. 229) that in certain Hirudinea the EndstUck arises 

 by an invagination of the epidermis. 



The middle ground between these extremes is the position taken by 

 Vejdovsky ('84 and '92). In early stages of Rhynchelmis ('84, p. 123), 

 on the posterior face of the dissepiment there is a large cell, from which 

 there is proliferated posteriorly a solid cord of cells. These cells later 

 form a double row and acquire a lumen. This becomes the glandular 

 portion of the organ, which therefore arises from the mesoblast. The 

 nephrostome appears independently on the anterior face of the dissepi- 

 ment, and later joins the glandular portion by piercing the dissepiment. 

 The cord of cells proliferated posteriorly from the dissepiment is met, at 

 a later stage, by an ectoblastic invagination in the form of a solid cord. 

 From this invagination is derived the lining of the end vesicle and the 

 efferent duct. This ectoblastic lining is, at a subsequent period of devel- 

 opment, surrounded by mesoblastic tissue in the form of a sheath. In 

 his later paper ('92, pp. 339-342) he reaffirms the results of his earlier 

 publication. This general plan of development, with slight modification 

 of details, holds, in his opinion, for the nephridia of all Oligochseta ('84, 

 p. 123), as also for Polychseta and Hirudinea ('92, p. 357). 



Vejdovsky's results are in agreement Avith those of Kowalevsky ('71) 

 and Boutchinsky ('81), and in part are confirmed by the work of several 

 other writers. It will be noticed that they do not depart widely from 

 Bergh ('88), except in the conditions at the peripheral end. 



After comparing these various papers it seems to me that Vejdovsky's 

 descriptions and figures are more convincing of accuracy of observation 

 and reliability of interpretation than are those of the writers who adopt 

 one or the other of the extreme views ; and yet it is not permissible to 

 disregard the work of such able investigators as Bergh and Wilson. If 

 we except the positive statements of Bergh, which lack the corrobora- 

 tion of later investigators, we may conclude that the evidence goes far 

 to show that both mesoderm and ectoderm share, though unequally, in 

 the development of the nephridium in Annelids, and therefore that, as 

 far as origin from germ layers is concerned, there is no insurmountable 

 obstacle to homologizing the nephridia of Chajtopod "Worms with the 

 antennal glands of Macruran Crustacea.^ 



1 Postscript. — Bergh ('99) has repeated Vejdovsky's work on Rhynchehnis, 

 but disa<?rees with him in regard to the conditions and the interpretation to he put 

 on tliem : " Nach alledeni nieine ich meine urspriingliclie These, dass Tricliter-, 

 Sehlingen- und Endahsclinitt bei den Oligochaten aus einer einheitlichen Anlage 

 hervorgehen, audi fiir Rhynchelmis festhalten zu miissen " (p. 44C). 



