24 ARTHUR E. SHIPLEY. 



the Hirudinea, there is direct communication between the coelom 

 and the blood vessels. 



The body-cavity of Sipunculus is developed as a split in the 

 mesoblastic bands; the cells lining it give rise to the generative 

 products ; and the nephridia open at their internal ends into it. 



The blood vascular system arises late. Hatschek' describes its 

 first origin during the metamorphosis of the larva, lying on the 

 dorsal side of the alimentary canal. Although his description is 

 not very detailed, there is nothing to shew that we have here to 

 do with anything more than a normal blood vessel. 



In the adult the main longitudinal vessel lies well surrounded 

 by connective tissue, and between two of the longitudinal vessels ; 

 it contains usually only blood corpuscles, which are exactly like 

 those found freely in the body-cavity; but in individuals which 

 are sexually ripe, spermatozoa and ova are often found in it. The 

 openings, by means of which the cavity of this vessel communi- 

 cates with the coelom, can be seen if the vessel be dissected out 

 and exposed under a microscope ; and further, Vogt and Yung''' 

 state that it is easy to inject the former from the latter. 



Another group which stands far apart from both the Hirudinea 

 and the Gephyrea, and in which communications exist between 

 the vascular system and the coelom, or at any rate with part of 

 it, is the Echinodermata. Here, according to the observations of 

 Hamann and Koehler, in Spatangids at least the blood system 

 is in communication with the water vascular system, embryo- 

 Ingically a part of the coelom and developed from an outgrowth 

 of the body-cavity. And according to the French school of 

 naturalists who have worked at this group, and amongst whom 

 Perrier is the most prominent, this connection may be extended 

 to the whole group of the Echinodermata. 



Finally, in the class Vertebrata we again find the body-cavity, 

 which is admittedly coelomic in nature, in communication with 

 the vascular system, which is to some extent at any rate archi- 

 coelomic. The means of communication is through the lymphatic 



1 B. Hatsebek, " Ueber Entwicklung von Sipunculus nudus." Arbeiten aus 

 dem Zoologischen Institut. Wien, Bd. v. p. 33. 



* Vogt and Yung, " Lehrbuch der praktischen vergleichenden Anatomie." 



