DEVELOPMENT OP THE OAPE SPEOIES OF PERIPATUS. 491 



what in other animals would be called a pseudocode. For this 

 second system of cavities and its devivates I shall therefore use 

 the words pseudoccele or vascular space. 

 My results can be summed up as follows : 



1. The adult body cavity comes entirely from pseudoccele. 

 The enterocoele has no part in its formation. 



2. This statement applies also to the heart and pericardium. 

 These are both pseudoccelic^ and have nothing to do with 

 enterocoele. 



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. 13) 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. 13, 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 

 ccelom 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 different. 



KenneFs observations of the fate of the so-called median 



1 This Arthropodan character was first pointed out to me by Professor 

 Lankester. I have never seen attention called to it iu any works or memoirs 

 on this subject. 



