26 CCELOM AND HsEAfOCCEL 



subsequent development of this space in Peripatus, there can cer- 

 tainly be derived some justification for the view (which has from 

 time to time been expressed by various morphologists) that a space 

 between primitive endoderm and ectoderm formed by the accumu- 

 lation of liquid in that position, and spoken of as the " blastocoel," 

 is the origin, the point of departure, so to speak, of the blood- 

 vascular system. We cannot, however, consider that this ques- 

 tion has been yet brought to a probable solution. Whatever its 

 ancestral origin, it is abundantly clear from Mr. Sedgwick's draw- 

 ings and statements that the hsemoccel thus formed is entirely 

 independent in its origin of the ccelom, with which it never 

 acquires any kind of connection. Observations tending to extend 

 Sedgwick's discovery to the embryological history of Crustacea 

 and some other Arthropoda have been made since his publication 

 by other observers (see Allen, Quart. Jour. Micr. Sci. vol. xxxiv. 

 1893, p. 403). 



At the meeting of the British Association in Manchester in 

 1887 having been confirmed by Sedgwick's demonstration in the 

 speculations to which I had been led by the consideration of other 

 facts I formulated a general theory of the origin of the hrcmoccel 

 of both Mollusca and Arthropoda by an excessive swelling of the 

 non-arterial portions of the vascular system which, in an earlier 

 ancestral form, had been provided throughout with tubular capil- 

 laries and veins. A report of this communication appeared in 

 " Nature " of March 1888, and was reproduced with some additional 

 remarks and a diagram (Fig. 12) used on the occasion of the 

 original communication, in the Quart. Journal of Micros. Science, 

 1893, vol. xxxiv. p. 427. This theory I now call the theory of 

 Phlebcedesis. 



As stated in the paper above cited, the theory thus named is 

 as follows : " That the system of blood-containing spaces pervad- 

 ing the body in Mollusca and in Arthropoda is not, as sometimes 

 (and indeed usually) supposed, equivalent to the ccelom or peri- 

 visceral space of such animals as the Chsetopoda and the Verte- 

 brata, but is in reality a distended and irregularly swollen 

 vascular system the equivalent of the blood-vascular system of 

 Chaetopoda and Vertebrata." The name haemoccel was proposed 

 by me for this phlebcedetic space or cavity, and was subsequently 

 adopted by Sedgwick in his detailed account of the development 

 of ccelom and blood space in Peripatus. At the same time I 

 showed from injections and silver impregnations of Anodon, 

 Cephalopods, Astacus, and Limulus, that true capillaries are in 

 certain regions of the body in both Mollusca and Arthropoda 

 more largely developed than is generally supposed. I showed 

 that the far-spreading tubules of the organ o* Keber in Molluscs, 

 and probably also a system of spaces in the connective tissues of 



