242 



A. IZUKA. 



fact that the so-called " Übergangstheil " of the alimentary canal, in the 

 retracted state of the proboscis, is for the greater part contained in the 

 region of those segments. The said modification consists in the following 

 three points : i) The five pairs of the dorso-vcntral vessels belonging to the 

 segments in question do not send off capillary branches into the alimentary 

 canal but stand entirely free of the latter. 2) Each of the dorso-vcntral 

 vessels, instead of uniting with its fellow of the opposite side before 

 opening directly into the dorsal vessel, proceeds to the lateral vein of its side 

 and separately joins it at a point inside of the dorsal longitudinal muscle and 

 shortly before it rounds the inferior edge of the latter. 3) The five pairs 

 of the origin of the lateral veins from the dorsal vessel, instead of there 

 being one pair to each of the segments, are successively shifted backwards 

 so to say and are all situated in the space of the 8th and 9th segments ; the 

 results being that the dorsal vessel in the 5th-7th segments is seen to bear 

 no lateral veins ; that the five successive dorso-ventral vessels of either side, 

 after starting from the ventral vessel in the usual manner, run up more or 

 less Obliquely backwards, etc. In all other points the vascular arrangement 

 in the segments is essentially the same as in the more posteriorly situated 

 segments. 



Now as to the blood-vessels in the anteriormost parts of the body, 



i. e., in the segments ist-4th. In each of these four segments, the dorsal 



vessel v., woodcut) gives off a pair of lateral branches leading blood 



from that vessel into the so-called " Wundernetz " or the rete mirabile (r.m ). 



There are thus in all four pairs of afferent vessels to the rete, of which there 



is one on each side and which is formed by the splitting up of the said 

 afferent vessels into a continuous close-meshed network The rete gives 



Diagrams showing the 

 anterior portion of the 

 circulatory system. 



A, Dorsal view. 



B, Lateral view. 



,p.nw. 



r.m.- 



