470 



Scientific Proceedings, Royal Dublin Society. 



The nephridia themselves appear to be of mesohlastic origin. 

 It is possible that the archinephros extended throughout the 

 greater length of the body, as in Chsetopod Worms, but that in 

 time an anterior section (pronephros) came to be developed earlier 

 than the posterior portion (mesonephros). 



The precociousness in the development of the segmental duct 

 in ontogeny is not necessarily a difficulty, as it can be paralleled 

 by many other organs. 



On the hypothesis just sketched out, the nephridia always open 

 by their original epiblastic pores — primitively, directly to the ex- 

 terior ; secondarily, into a canal separated from the epiblast : also 

 the archinephros could be equally effectively functional throughout 

 the whole period of its modification. 



List of Papers referred to in the foregoing Paper. 



1. Balfour, F. M. 



2. Flemmtng, W., 



3. Gadow, H., . 



4. Gassee, E., . 



5. Hensen, V., . 



6. Johnson, A., . 



Treatise on Comparative Embryology, vol. ii., 

 1881. 



"Die ektoblastiscke Anlage des Urogenital - 

 systems beim Kanmchen." Arch. f. Anat. 

 u. Phys.-Anat. Abtheil, 1886. 



" Bemarks on the Cloaca and on the Copu- 

 latory Organs of the Anmiota," Proc. Roy. 

 Soc, 1886. 



" Zur Entwicklung von Alytes obstetricans." 

 Sitzungsber. d. Marburger Naturgesell, 1882. 



" Beobachtungen iiber die Befracktung und 

 Entwickelung des Meerschweinchens und 

 Kaninchens," Arch./. Anat. u. Phys., 1875. 



" On the Fate of the Blastopore and the 

 Presence of a Primitive Streak in the 

 Newt (Triton cristatus)," Quart. Joum. of 

 Micr. ScL, xxiv., 1884. 



