waite: antennal glands in homarus americanus. 195 



Granting, then, that in the antennal glands of Macrura and in the 

 nephridia of Chaetopoda both ectoderm and mesoderm are involved, can 

 these organs be compared part for part '? 



The chief point is to determine in each case the boundary between 

 the ectodermic and mesodermic constituents in the two sets of organs. 

 Where is this in the antennal gland of Macrura 1 In Homarus, as I 

 believe I have shown, it lies where the luruina of the endsac and of the 

 ectodermal sac (labyrinth) become confluent. Kingsley's results ('89, 

 pp. 29, 30, Figs. 61, 74) in Crangon seem to me to be capable of the same 

 interpretation, the mes-ectal line being at the junction of endsac and 

 ectodermal sac (canal). Boutchinsky's ('95) results on Gebia, since 

 they do not go beyond the earlier embryological stages, are not so 

 precise, but I find nothing in his descriptions or figures irreconcilable 

 with my conclusion, that the epithelium lining the endsac is also of 

 mesodermic origin, while that lining the labyrinth is derived from the 

 ectoderm. 



There is difference of opinion as to the corresponding boundary in the 

 nephridia of Annelids. In the permanent nephridia of Rhynchelmis, as 

 well as all other Annelids, according to Vejdovsky ('84 and '92), the 

 lining of the efferent duct and of the contractile endsac is, as has been 

 said, ectoblastic, whereas all the glandular part and the nephrostome are 

 mesoblastic in origin. Wilson ('89, p. 425), as we have seen, concludes 

 that the nephrostome and the investing peritoneal sheath of the glandu- 

 lar portion are alone mesoblastic, whereas the epithelium lining the glan- 

 dular portion, the duct, and the end vesicle are ectoblastic, arising from 

 the " nephric cord." Finally, Bergh ('88, p. 230, '90, p. 501) concludes 

 that in Criodrilus and Lumbricus the entire organ is mesoblastic, there 

 being no ectoblastic constituent whatever. Thus according to Vejdovsky 

 the mes-ectal line is at the junction of the glandular region and the 

 efferent duct ; according to Wilson it is at the base of the nephrostome, 

 and according to Bergh the gland presents no such line. 



It seems impossible to draw any satisfactory conclusion from this con- 

 flicting evidence. These differences of opinion are not solely explicable 

 upon the assumption of differences of methods in accomplishing the re- 

 sult in different worms, for all of these observers have worked and based 

 their conclusions in part iipon Lumbricus. The only point of complete 

 agreement is that the nephrostome is mesoblastic. 



If it is impossible to determine so fundamental a question as where 

 mesoblast ends and ectoblast begins, it is idle to attempt more detailed 

 comparisons. In the present unsettled state of knowledge as regards the 



