74 THE CHANGES FROM STAGE A TO P. 



3. The only products of the enterocoele cavity are : — (a) 

 The nephridia. (b) The generative glands and their ducts. 



4. The nephridia do not open either in the embryo or in the 

 adult into the body cavity proper (i.e. in Peripatus the 

 pseudoccele), but into a vesicle in each appendage which has 

 hitherto been unnoticed. 



These results, when taken in conjunction with the following 

 peculiarities of Arthropod organisation, viz. the feeble deve- 

 lopment of the somites, the apparent absence of nephridia, 

 the vascular character of the pericardial cavity, and the posses- 

 sion by the heart of lateral ostia opening into the pericardium,^ 

 will not be without interest to morphologists. 



Kennel (No. 29.) was the first to point out that the median 

 chamber of the body cavity and the pericardial chamber were 

 not products of the enterocoele ; but Kennel erred in supposing 

 that the cavities in the legs and the so-called lateral sinus 

 (No. 29, p. 202) were derived from the somites. In his later 

 memoir he apparently gives up this view so far as the lateral 

 sinus is concerned, but still maintains that a portion of the 

 coelom becomes broken up by muscles, &c., and persists as the 

 body cavity of the legs. In this, I think, he is mistaken, but 

 it must be borne in mind that he has worked at a different 

 species in which it is possible, though not likely, that the 

 development of the structure in question may be diflferent. 



KenneFs observations of the fate of the so-called median 

 divisions of the somites and of the origin of the generative 

 tubes, pericardial cavity, and heart, differ, as will be seen, con- 

 siderably from mine. His account, however, seems to me to 

 lack precision, and I cannot help thinking, especially when I 

 consider that he has altogether confounded the nephridial 

 vesicles of the adult with the leg body cavity (see below), that 

 he has erred here also. 



In my preliminary paper to the Royal Society (No. 50) I 

 also made the mistake of supposing the leg cavities were 



' This Aithropodan character was first pointed out to me by Professor 

 Laukester. I have never seen attention called to it in any works or memoirs 

 on this subject. 



