22 ARTHUR E. SHIPLEY. 



is formed laterally in each somite. One pair of these form the 

 ovary and seven pairs become testes. According to Nusbaum the 

 tunica of the generative glands is formed at the expense of the 

 mesoderm. This doubtless buds off corpuscles, just as it does into 

 the sinus, and thus forms the colourless corpuscles which Bourne 

 found in the fluid surrounding the true ovary. Nusbaum traces 

 the oviduct and vas deferens back to nephridia. 



I have attempted so far to shew firstly that there is no doubt 

 that the old statements with regard to the blood system of Leeches 

 being in communication with the sinus system is true, and secondly 

 that the sinus system is coelomic in nature. So that with regard 

 to the group Hirudinea, the vascular system is undoubtedly in 

 communication with the coelom. 



Let us now turn to the Nemertines, the second group of 

 animals mentioned by Sedgwick as forming an exception to the 

 rule that the blood system is independent of the coelom. 



The nephridial system of these animals is not so definite in its 

 arrangement as amongst the Hirudinea. Oudemans* has examined 

 it in a great number of forms, and I have to some extent been 

 able to confirm his observations. In his summary at the end of 

 his paper he states, " the nephridial system of the Nemertea 

 consists of one or more canals, directly communicating, or not, with 

 the vascular system, provided, or not, with cilia, and communicating 

 with the exterior by means of excretory ducts." 



But when we come to consider the nature of these spaces 

 which contain blood, and in which the internal end of the 

 nephridium is sometimes situated, we shall see that they differ 

 considerably in their fundamental origin from the sinus system 

 of the Hirudinea. 



In his valuable work on the embryology of Lineus obscurus, 

 Hubrecht^ points out that the blood vascular system together 

 with the proboscidian cavity represents the last remnants of the 

 archicoel or segmentation cavity. Hubrecht has proposed the 



1 A. C. Oudemans, " The Circulatory and Nephridial Apparatus of the Ne- 

 mertea." Q. J. M. S. less. Supplement. 



- A. A. W. Hubrecht, " Contributions to the Embryology of Nemertea." 

 Quarterly Journal of Microscopical Science, Yol. xxvi. p. 417. 



