267 



float a great number of corpuscles. In the Oligochseta, the 

 terrestrial and fresh-water forms, the perivisceral cavity com- 

 municates with the exterior by large convoluted ciliated 

 ducts, and a closed vascular system is constantly present in 

 addition, containing a solution of haemoglobin. In many 

 Polychseta there is no shutting off from the perivisceral cavity 

 of a closed vascular system. 



In leeches the cavity is reduced to a system of fine vessels 

 by the blocking up of its chief bulk with cellular tissue; it is 

 as though the corpuscles in the perivisceral fluid of Chseto- 

 pods became connected with one another, and aggregated into 

 a continuous mass. The properties of the perivisceral liquid 

 of Chsetopods, and its relation to the parenchyma of leeches 

 and trematods, must cause us to regard it as something more 

 than a great excretory cavity, and make it rather com- 

 parable, but only by way of analogy, to such an organ 

 as the blood-lymph system or Hsemochyle of Vertebrata. 

 This being the case, the origin of the corpuscles which 

 float in this perivisceral liquid becomes important in rela- 

 tion to the origin of corpuscles, which pass in or out of 

 the vertebrate hsemochyle system, and their analogy may 

 suggest explanations of facts observed in the one or the other. 

 That there is any homology, in the sense of homogeny, i. e. 

 genetic community of origin, between these vascular systems 

 or those of any of the invertebrate groups and the Vertebrata, 

 must not be supposed. 



In several genera of the Oligochseta I have carefully 

 examined the corpuscles of the perivisceral fluid, and endea- 

 voured to trace their origin. There is no doubt that the majority 

 of them are detached from the layer of large cells containing 

 yellow granules, which surround the alimentary tube and 

 blood-vessels. (PI. XVII, fig. 5.) This layer of cells varies 

 very much in its form in different genera, and is directly 

 continuous through the layers of cells which enclose the seg- 

 ment organs, or, as in Lumhriculus, through those which 

 enclose the lateral blood-vessels also, with the endothelial 

 cells of the body-wall. In Lumhriculus the cells on the 

 lateral blood-vessels have the same coarse yellow granules 

 as those on the alimentary canal and on the dorsal vessel, 

 seen in all Oligochseta without exception. In Limnodrilus 

 the cells on the intestine are exceedingly long and large, and 

 have the character of Becker-zellen — goblet-cells — very well 

 marked. (PI. XVII, fig. 4.) The cells of the hepatic tunic of 

 the intestine, as it is sometimes termed, exhibit this form at one 

 period of their development in all Oligochseta; and it is pro- 

 bable that they discharge their contents or a part into the 



