70 ALFEED GIBBS BOUENE. 



'* quadrillage'^ of Perrier (9, p. 491) and Jaquet (6, p. 345), 

 is so dense a network that it may be regarded as a blood sinus 

 interrupted at certain spots ; the interspaces are in certain 

 places even smaller than the vessels which surround them. 

 The meshes are not so regularly rectangular as they appear to 

 be in some other genera ; they are not equally so, moreover, 

 in all regions of the intestinal wall. Near the typhlosole and 

 also along the intersegmental lines the longitudinal portions 

 of the network are specially developed, and the meshes fairly 

 rectangular ; in other regions they are less regular. The net- 

 work is continuous from segment to segment^ and across the 

 dorsal and ventral median lines in each segment. The vessels 

 are largest and the interspaces smallest over the typhlosolar 

 region. There is indeed so much blood in this region that 

 when the intestine is opened the typhlosole strikes the eye at 

 once as a longitudinal band of red colour, noticeable even when 

 the whole surface appears red. I have seen the vessels so dis- 

 tended that the interspaces were hardly recognisable. With 

 the slight exceptions mentioned above, there is not very much 

 difference in calibre among the vessels composing the network. 

 All the vessels in any particular region may be distended or 

 the reverse, but that is all. This internal network is directly 

 connected with the dorso-intestinal vessels. 



The external network is very different. The vessels are of 

 very various calibres. There are large vessels which divide 

 into small branches, and these subdivide and so on ; the 

 smallest branches form a complete network. These networks 

 are arranged segmentally, and are not continuous, as networks, 

 that in one segment with that in another, as is the case with 

 the internal network. The network in each segment is con- 

 tinuous over the ventral median line, but not over the dorsal 

 region. At very numerous spots little branches from the 

 external network penetrate the intestinal wall and open into the 

 internal network. The vessels of the external network have 

 always clearly defined but very thin walls, do not seem capable 

 of distension, and do not form anything like so close a net- 

 work as the internal one. The vessels of the external network 



