20 ARTHUR E. SHIPLEY. 



funnel of the nephridium, and in the sac they disintegrate and are 

 eventually thrown out from the body. In Asteroideae, where there 

 are no nephridia, the corpuscles work their way out through the 

 body-wall. 



We owe our knowledge of the paths by means of which the 

 fluid passes from the blood vessels into the coelom chiefly to 

 Lankester and Bourne. Besides the direct communications which 

 exist in the Rhyncobdellidae, there is the communication by means 

 of the botryoidal tissue which is seen at its best in the Gnatho- 

 bdellidae. A fragment of the brown tissue of a Leech shews at 

 once the connection of the lumen of the botryoidal tissue with 

 that of the thin walled vessels. And my sections through Clepsine 

 and Hirudo shew in numerous places the large openings by means 

 of which the botryoidal tissue is put into communication with the 

 sinuses, soinetiraes a continuous coagulum being found, lying half 

 in one and half in the other system of spaces. 



The same kind of blood is found in both the true vessels and 

 the sinuses, except that, as Bourne points out, certain large 

 corpuscles which occur in the sinuses of Clepsine and Pontobdella 

 are not found in the blood vessels, being, as he suggests, too large 

 to pass through the communicating channels. 



The contraction of the dorsal vessel in its sinus can be seen 

 without difficulty, and I have often watched the ventral vessel 

 contract, sending the blood from before backward, whilst the 

 current in the sinus surrounding the vessel flowed in the reverse 

 direction. The fluid and corpuscles in both vessels and sinuses 

 being apparently identical. 



The foregoing facts fully corroborate Bourne's statements that 

 the nephridia open into the sinuses, whicli in their turn are in 

 communication with the blood vessels, and which contain the 

 same fluid as the vascular .system. With regard to the embryo- 

 logical nature of these spaces we are largely indebted to the 

 researches of Nusbaum*. He describes in Clepsine the meso- 

 blastic bands dividing into 33 somites. Each of these somites 

 acquires a cavity which gradually increases in size. The walls of 



1 Archives Slaves dc Biolorjk, Vol. 1, pp. 320 and 539. 



