34 CCELOM AXD RENAL ORGANS 



a remarkable association of nephridium and coelomoduct to form a 

 complex renal organ. 



The theoretical conception that the renal tubules in the 

 animal series are of two distinct kinds, a more primitive and a 

 secondary, dates back to Gegenbaur. Continually the attempt 

 has been made to separate in a distinct category the nephridia 

 formed by a linear series of perforated drain-pipe cells from other 

 so-called nephridia with a lumen surrounded by many cells. It 

 cannot be said that the provisional doctrine of a single category 

 of renal organ in the entire series of Ccelomoccela, for which I am 

 responsible, had obtained very general assent amongst critical 

 embryologists, although the general use of my term " nephridium " 

 for all sorts of renal tubes in all classes of animals might lead to 

 the assumption that such a community of origin was accepted. 

 The necessity for revising the doctrine of uniform origin of renal 

 tubes was pressed upon Goodrich by the careful determinations 

 of the origin of these structures in some cases from ectoderm, in 

 other cases from ccelom, by various embryologists in later years. 

 Thus Sedgwick says in his paper on the development of Peripatus 

 in 1888: "It is important to notice that in Peripatus the 

 nephridia are parts of the coelom just as they are in Elasmo- 

 branchs. They are commonly spoken of in a manner which 

 implies that they have but little to do with the coelom beyond 

 opening into it. This way of speaking of them is calculated to 

 mislead. The nephridia are direct diti'erentiations of part of the 

 coelom" (Q. J. Micr. Sci. vol. xxviii. p. 391). On the other hand, 

 Vejdowsky has no less emphatically and conclusively shown that 

 the nephridia of certain Oligochieta are of ectodermic origin, 

 whilst Bergh and other observers trace them in many cases to 

 peculiar superficially placed mother-cells lying in a so-called meso- 

 blast, each of which by division gives rise to a single row of 

 cells — a nephridium. 



This difficulty is resolved by the recognition which we owe 

 to Goodrich of two categories of renal tubes : (a) The ccelomic 

 ctelomoducts, which are primarily genital sacs and ducts, and second- 

 arily acquire renal functions ; and (/') the nephridia, which are 

 primarily excretory tubules and only in the marine Cha^topoda 

 acquire functions in connection with the crelomoducts as genital 

 conduits (see Goodrich, loc. cif.). 



Thus, then, we arrive at a further stage in the theory of the 

 ccelom. The true nephridia so long supposed to have a 

 morphological connection with it are separated from it altogether. 

 The organs which really belong to it and are, in fact, only parts 

 of it, whether appearing as renal sacs or genital conduits, are the 

 cfolomoducts. The ctolom is now, as a final result of observation 

 and speculation up to the present date, to be conceived of as 



