of Oligochcetous Annelids. 95 



the genus Pachydrilus^ to which these forms with red blood 

 would be referable. 



5. Endothelium of the Perivisceral Cavity. — The peririsceral 

 cavity of the Oligochajta is lined with a more or less complete 

 cellular membrane, which is directly continuous with the 

 coarse-grained yellow cellular layer covering the large vessels 

 and alimentary canal. The continuity of this layer has been 

 hitherto overlooked. The whole endothelium, whether the 

 visceral or the parietal portion, casts ofl" its cells into the peri- 

 visceral liquid, Avhere they float. The large bladder-like cells 

 seen in Limnodrilus suiTOunding the coils of the segmental 

 organ, and figured by Claparfede, are simply continuations of 

 the general endothelium, and are to be seen in Tuhifex also. 

 The parietal endothelium is more complete in Limnodrilus 

 than in Tuhifex^ and the cells are large and clear, branching 

 and anastomosing with one another on the surface of the in- 

 ternal muscular layer of the body-wall. In one species, as 

 before mentioned, they are pigmented. In Tuhifex there are 

 very few cells indeed of the parietal endothelium on the mus- 

 cular surface ; but they are densely lodged in four grooves 

 running longitudinally and placed between the longitudinal 

 bands of muscular tissue. In Tuhifex the cellular elements of 

 the muscular tissue, as well as the cells of the parietal and 

 visceral endothelium, are shed into the perivisceral liquid. 

 This also takes place in other S^nui'ida?. In Cluetogaster 

 there is no parietal endothelium, and the septal muscular 

 fibres are branched cells with nuclei. In Nais^ cells similar to 

 those of the so-called hepatic tunic of the intestine are to be 

 seen fixed to the body-wall, representing the parietal endo- 

 thelium. 



6. Generative Organs of Tubifex. — M. Clapar^de gave a 

 very fair account of the genitalia of several Oligochgeta in his 

 ' Recherches,' adding much to what M. d'Udekem had done. 

 At the same time I have been led to differ veiy much from 

 Claparede on some important points. 



It is not correct to say that Tuhifex is simply hermaphro- 

 dite. What occurs here appears to occur also in other Limi- 

 colae, viz. that though both sets of organs are present, one sex 

 or the other predominates : thus it is usual to find an excess 

 of spermatozoa or an excess of ova. Some very instructive 

 specimens have come under my observation, in which the 

 organs in the ninth fasciculate segment, viz. the testes and 

 receptaculum seminis, were entirely undeveloped and not even 

 represented, whilst those in the tenth (viz. the ovary and male 

 efferent apparatus) were of full adult size ; many large ova, 

 ripe for deposition, were present, and the male efferent canal, 



