waite: antennal glands in homarus americanus. 191 



III. Theoretical Considerations. 



A. Homology of the Antennal Glands with the Nephridia of 



Annelids. 



Leydig ('60, p. 28) was the first to suggest that the antennal glands 

 of Crustacea and the nephridia of Annelids performed similar duties. 

 He, however, ascribed to both a respiratory instead of an excretory 

 function. Since that time there has been much discussion in regard 

 to the functional likeness of these organs in the two groups of animals. 

 Naturally, this consideration has led to the discussion of their possibly 

 being homologous. This discussion was inaugurated by Kowalevsky 

 ('71). Upon grounds of analogy, and from a comparison of the struc- 

 ture of the adult organs, it came to be pretty generally accepted that 

 this homology was valid. Confidence in this view was, however, shaken 

 by the publication of Reichenbach's ('77) description of the ectodermic 

 derivation of the antennal gland in Astacus. Kowalevsky (71) had 

 given proof of the mesodermic origin of the nephridia in Euaxes (p. 19) 

 and in Lumbricus (p. 25) and had formulated the germ-layer theory, 

 holding "that the homologies of the germ layers in different types 

 afford a scientific basis for comparative anatomy and embryology, and 

 must be recognized as the starting point for the proper understanding 

 of the relationships of the types " (p. 60). So great was the influence 

 of the germ-layer theory that the results of Reichenbach in deriving the 

 antennal gland of Astacus entirely from the ectoderm served, for the 

 time being, completely to check its comparison with the mesodermic 

 nephridia of Annelids. 



Grobben ('79) showed, however, that the shell gland of Moina was 

 in part mesodermic, and thus partially restored the grounds for homolo- 

 gizing it with the nephridia of Annelids ; but Ishikawa's ('85) evidence 

 that the antennal gland in Atyephira is derived solely from the ecto- 

 derm, and the conclusions reached soon after in Reichenbach's ('86) 

 memoir, — in which the ectodermic origin of the antennal gland in 

 Astacus was described and figured in detail, — not only reaffirmed the 

 obstacles to establishing a homology between the antennal glands and 

 the nephridia of Annelids, but also placed in different categories the shell 

 glands of Entomostraca and the antennal glands of Malacostraca. 



The contrary conclusions reached by Kingsley ('89) in his descrip- 

 tion of the development of the antennal gland in Crangon threw some 

 doubt upon the accuracy of the observations and interpretations of 



