TEANSVEESE SECTIONS. 57 



2. The peri-nephrostomial sinuses are easily recognised 



in sections which pass through the testes, on the 

 dorsal surfaces of which they lie. 



3. The lateral vessels are large and have distinct muscular 



walls. 



4. The capUlaries are very thin-walled tubes, the distribu- 



tion of which can easily be followed owing to the 

 contained blood. The intercellular plexuses of the 

 epidermis and of the nephridia should be specially 

 noticed. 



The capillaries are directly continuous in various 

 parts of the body with brown pigmented fibres, 

 similar to those of the dermis already described. 



5. The botryoidal tissue consists of a network of vessels, 



the channels of which are irregular in width and 

 the walls formed of large granular pigmented cells 

 which project as irregular rounded swellings. 



These curiously swollen vessels occur in great 

 abundance around the crop, immediately within the 

 longitudinal muscle-layer. They are in free com- 

 munication with the ordinary blood-capillaries. 



F. The Excretory Organs. 



The nephridia have already been fully described. The 

 details of their structure, and more especially the intracellular 

 network of ductules, and the intercellular capillary plexuses, 

 can be readily made out in transverse sections, and should 

 be carefully studied. The structural differences in various 

 parts of the organ should be noted, and particularly the 

 head of the testis-lobe, which lies in the peri-nephrostomial 

 sinus. 



G. The Beproduotive Organs. 



1. The testes are seen, if the section happens to pass 

 through them, as spherical sacs lying at the sides of 

 the ventral sinus, and containing groups of sperma- 

 tozoa in various stages of development. 



