On the Structure of Body- Wall in certain Earthworms, 89 



V. Note on the Structure of the Body- Wall in certain Earth- 

 ivorms. By F. E. Beddakd, Esq., M.A. (Oxon.), F.E.S.E., 

 F.Z.S. 



(Read 16th January 1884.) 



Although up to the present but few of the numerous genera 

 of earthworms have been histologically investigated, it appears, 

 from what is known, that the structure of the body -wall 

 varies considerably in detail in different types; all agree, 

 however, in possessing an outer epidermis which secretes a 

 thin chitinous cuticle, and two subjacent muscular layers, an 

 external transverse and an internal longitudinal. The present 

 note relates to the structure of the body-wall in the two 

 genera, Perionyx and Ferichcetcc, 



In Perionyx the epidermis closely resembles that of the 

 common earthworm; it is composed of a single layer of 

 delicate elongated cells, among which may be distinguished 

 a number of larger granular cells, connected with the exterior 

 by a fine pore, which passes through the outer chitinous 

 cuticle. The structure of the epidermis in the common 

 earthworm has recently been carefully studied by Dr Horst ^ 

 and Dr v. Mojsisovics,^ and both these observers agree in 

 stating that it is only vascular in the region of the clitellum. 

 In Perionyx, on the contrary, the terminal branches of the 

 blood system penetrate within the epidermis of the general 

 body surface. With the exception of Pleurochceta, a new 

 genus lately described by me,^ this is the only example of 

 the phenomenon among the Oligochseta, and it is not a little 

 remarkable that a structural feature of such obvious physio- 

 logical advantage should be present in one genus and absent 

 in another, especially when we consider that there can be no 

 great difference between various species of earthworms in 

 mode of life and in their physiological needs. There can be 

 no possible doubt that this intra-epidermic vascular plexus 

 is entirely unrepresented in the common earthworm as well 

 as in the two genera Urochceta and Pontodrilus, upon which 



1 Tijdschr. d. Xedeiiandscli. dierk. Yer., Deel iii., afl. 1. 



2 Sitzungber. Akad. Wiss. Wien, 1877. 



3 Trans. Roy. Soc, Edinb., vol. xxx., pt. 2. 



