CCELOM AND VASCULAR SYSTEM IN THE LEECH. 487 



vessels of the botryoidal tissue arising from branches of the 

 lateral vessels; (2) an intermediate layer, being the capillaries 

 winding amongst the muscles, derived from the same vessels, 

 and communicating with the botryoidal vessels; (3) the super- 

 ficial cutaneous layer, divided into a right and left plexus, 

 communicating with capillaries arising from the intermediate 

 layer, and also supplied by fine branches from the sinuses. 

 This last section, the cutaneous plexus, has been shown by 

 Professor Lankester to extend into the epidermis itself (8). 



The results of my observations agree fairly closely with 

 Gratiolet's description, the chief diff'erences being with regard 

 to the supply of the capillary systems. 



It has already been mentioned that the latero-lateral and 

 the latero-dorsal vessels give off small branches passing radi- 

 ally outwards to the skin. So far as I have seen, these radial 

 vessels have no direct communication either with the botryoidal 

 tissue, or with the intermediate layer of capillaries amongst 

 the muscles, but pass right through these to near the epidermis 

 (fig. 7). Here they branch, forming what I shall call annular 

 vessels,^ running round a little below the epidermis, on the 

 one hand towards the median dorsal line, and on the other 

 towards the ventral surface (figs. 4 and 7). 



At short intervals the annular vessels give off small branches 

 to the delicate epidermal plexus. Although the annular vessels 

 of the right side never directly join those of the left, two such 

 vessels from different branches of the latero-dorsal may run 

 into each other, forming a complete loop (fig. 7). 



At the sides these vessels may pass round, describing more 

 or less complete semicircles, and reaching sometimes to the 

 ventral surface. Exceptionally, as shown in fig. 4, they may 

 turn inwards again so as to open into the ventral botryoidal 

 channels. 



Now the superficial epidermal plexus, into which 

 the small branches of the annular vessels open, is 



1 These annular vessels may be the small vessels termed " branches verti- 

 cales superficielles " by Gratiolet, and described as branching at both ends 

 into the plexus. 



