1883.] Contributions to the Anatomy of the Hirudinea. 353 



Dorso-ventral and radial muscles. 



Muscles in the wall of the alimentary canal. 



With regard to the pharynx and its muscles, the protrusible 

 pharynx of the Rhyncobdellidee is to be regarded as representing the 

 whole body in that region, rather than as merely a central region ; 

 when protruded it is in fact an anterior portion of the body. The 

 manner in which it protrudes and recedes into a temporary sac 

 would suggest this, but comparison between its structure and the 

 structure of the whole anterior portion of the body in the Gnatho- 

 bdellidse shows that such is the case. This can only be made clear 

 hy a series of figures which the author gives. 



Muscles developed in the walls of blood-vessels. 



Muscles developed in connexion with the generative glands. 



Muscles in the walls of the vesicle of the nephridium. 



Muscles developed in the skin. 



Histological Characters of the Muscles. 



The muscles are formed of elongated cells arranged either in bundles 

 or lying singly. 



These cells may be much branched ; such branched cells occur upon 

 the wall of the alimentary tract, and among the dorso-ventral muscles. 

 The cells consist of a cortical and medullary substance, greatly 

 differentiated from one another. The medullary substance is granular 

 and lodges a large oval nucleus in all cases. 



Connective and Vasifactive Tissue. 



The author has worked out the histology of the connective sub- 

 stance, and traced its various metamorphoses throughout the group. 



The matrix consists of a jelly-like substance, which varies much in 

 amount in different genera ; its amount determines the "limpness " or 

 rigidity of the leech. Hcemopis and Aulostoma, whose bodies are 

 always t£ limp," possess a great quantity, while Clepsine and Nephelis, 

 whose bodies are rigid, possess very little. 



In the matrix are embedded indifferent corpuscles. 



The corpuscles undergo certain metamorphoses : — 



1. Entoplastic metamorphosis — the cell preserving a rounded form 

 — Vacuolated cells — Fat cells. 



A semi-fluid substance accumulates in droplets in the cell, giving it 

 -a reticulately vacuolated appearance ; such cells resemble Waldeyer's 

 plasma cells. They are very common in Pontobalella. 



Fat globules also accumulate, and running together form fat cells, 

 similar in character to the fat cells of Yerfcebrata. This occurs in 

 Clepsine and Piscicola. This substance formed presents all the cha- 

 racters and reactions of fat. 



vol. xxxv. 2 A 



