308 



den entsprechenden Theilen niederer Wirbelthiere bieten. Eine aus- 

 führliche Arbeit, welche das centrale Nervensystem der Vögel und an- 

 derer Thiere umfasst, wird in kurzer Zeit erscheinen, gleich wie die 

 »Untersuchungen über die embryonale Entwickelung des Vogelhirns«. 



3. On the body-cavity (coelom) and nephrìdia of Platyhelmia. 



By E. Ray Lank e st er, Professor in University College, London. 



In his valuable memoir »Recherches sur l'appareil excréteur des 

 Tréraatodes et des Cestodes. Deuxième partie« published in the Ar- 

 chives de Biologie, Tome II. Fascicule 1. M. Julien Fraipont quotes 

 and discusses the views which I have put forward as to the existence of 

 a body-cavity in the Flat-worms, in my article on the »Cell-layers of 

 the embryo« (Annals and Magaz. Natural History, 1873). 



As a matter of fact (though I had not succeeded in observing the 

 exceedingly important facts made known by M. Fraipont) I had been 

 led by investigation of various species of Cercaria and of the trans- 

 parent Aspidogaster and of Caryophyllaeus (L eu ck art's Archigetes) 

 to the theoretical conclusion which M. Fraipont has himself estab- 

 lished, — namely that the canalicular system which communicates with 

 the exterior in these animals consists of two parts, a part which repre- 

 sents the excretory organ or ,nephridium^ and is nearer to the external 

 pore and a part which consists of that portion of the canal system furthest 

 removed from the pore, constituting a net-work Avhich represents the 

 coelom or body-cavity. This view I expressed as plainly as I was able 

 in the article in question and also in »Notes on Embryology and Classi- 

 fication« 1877. p. 38 where are the words »The nephridia in Rotifers and 

 Turbellarians and Trematods are the ciliated canals, though in the Flat- 

 worms it is impossible to say where in the canal systpm ,nephridium' 

 ends and , coelom' begins«. 



In thus interpreting a part of the fine canal system which I, in 

 common with other observers , had studied in the more transparent 

 forms of Platyhelmia as representing the coelom or body-cavity of Coe- 

 lomata, I have found myself in opposition to H a eck el and in a criti- 

 cism by him upon my views, the objection was very justly urged that 

 we did not possess any knowledge of the development of the canal 

 system in Platyhelmia which warranted the assumption that any part 

 of it was the representative of the coelom of other animals. 



It was therefore a matter of special satisfaction to me to find my 

 supposition converted into an established fact by Bütschli's disco- 

 very of the terminal ciliated bodies of the nephridia of Cercaria. 

 Bütschli's discovery of these bodies which had escaped all previous 



