NOMENCLATURE OF THE CCELOM 35 



originally one or more pairs of detached or coalesced sacs originat- 

 ing ancestrally as pouches of the archenteron from which they 

 become shut off, having for their primary function the develop- 

 ment upon their walls of the male and female reproductive cells, 

 and communicating with the exterior by simple or funnel-like or 

 tubular extensions of their own walls. They serve primarily as 

 the sites of the development of the genital products, but secondarily 

 may have a renal excretory function localised in a part of their 

 epithelial lining cells. Very generally they give rise to extensive 

 perivisceral and pericardial sacs, which remain continuous with 

 the original outwardly opening portions, or may be nipped off 

 from them and from each other. 



(e) Nomenclature of the Parts and Derivatives of the Coelom. 



The various terms which are appropriate to, and useful in, the 

 discussion of the coelom and its subdivisions require a brief special 

 statement. The terms may be best defined in a series of proposi- 

 tions which are more or less of the nature of a sketch of the evolu- 

 tion of the coelom. 



1. The primitive coelom may be called a " PROTOCCELOM " 

 (Goodrich). It is probably multiple. Each protocoelom is in its 

 nature a GONOCCEL (Goodrich), that is to say a coelomic pouch, 

 the epithelial walls of which produce ova or sperm or both. 



2. Probably at a very early period each protocoelom acquired 

 a " CGELOMOPORE " (Goodrich) or opening to the exterior. 



3. The part of the protoccelom connected with the pore 

 frequently becomes narrow and funnel-like, and is then to be dis- 

 tinguished as a " CCELOMODUCT " (Lankester), whilst the rest of 

 the coelom may persist as simple gonocoel or undergo further 

 developments. 



4. Two (right and left) or more gonoccels may fuse and give 

 rise to an extended coelomic cavity, the walls of which for the 

 greater part are not concerned in the production of gonad cells. 

 Such an extended cavity is generally known as a "perivisceral 

 cavity " or " perivisceral coelom." It may be called the " SYN- 

 CCELOM " (Lankester). 



5. The syncoelom frequently develops renal-excretory functions 

 in the cells of its lining epithelium. 



6. In segmented animals where pairs of "gonoccels" are 

 repeated in each segment, some may retain the function of pro- 

 ducing gonad-cells, whilst others become modified as renal-excretory 

 sacs. These latter are to be called " UROC(ELS " (Goodrich). 



7. In some cases, e.g. some Mollusca, the gonocoel of one side 

 of the body will retain its relation to the generative function, 



