520 :MR. a. D. MICHAEL ON THE 



extremely well developed in Bdella. It forms a thick tendinous plate, which, in 

 B. vulgaris, shows signs of being formed by the compression of a sac ; at all events, it 

 has thick upper and under walls, which in a transverse section of the creature show a 

 narrow but distinct lumen between them ; which, however, is crossed by " ties " between 

 the upper and under walls. The endosternite lies between the ventriculus, which is 

 above it, and the hind part of the brain (not quite its posterior end), which is below it. 

 It forms a point of attachment for numerous muscles, principally the great muscles 

 of the legs, which are tlie largest in the body. The endosternite is slung from above 

 by dorso-ventral muscles and muscles from the lateral surface of the body, and by 

 connective tissue ; the muscles converge to it from all sides. 



The Musculature. 



A large number of the muscles have been described in connection with the various 

 organs ; I do not propose to enter into any exhaustive desci'ij)tion of the remaining ones, 

 particularly as some of them are figured by Karpelles ; but there are some which I may 

 mention. I have not draAvn any of the musculature except that incidental to other 

 figures, because doing so would have involved having another plate. All the muscles 

 described below are paired muscles corresponding on the two sides of the body. 



LonyitucUnal 3fuscles. — From the dorsal cuticle nearly above the fourth leg, and 

 almost close to the hind fasciculus of dorso-ventral muscles, two bundles of powerful 

 muscles arise ; both of these are horizontal muscles running for their whole length almost 

 immediately under tlie dorsal cuticle. The anterior of these bundles runs forward above 

 the alimentary canal and the paired salivary glands ; it spreads out and is inserted partly 

 in the dorsal cuticle about where the dorsum begins to sink toward the rostrum, partly 

 in the upper proximal edges of the mandible, and partly in the cuticle behind the lower 

 proximal edge of the mandible The other bundle runs backward, and is inserted in the 

 dorsal cuticle near the posterior end of the hoAj ; thus these two sets of horizontal 

 muscles, starting from one point, embrace between them almost the entire length of the 

 body, except the rostrum. They manifestly serve to compress and shorten the body 

 longitudinally and to retract the rostrum. 



Prom the dorsal cuticle just in front of the ventriculus two fasciculi of numerous 

 muscles, much sligliter than those last described, arise ; one of these is inserted in the 

 rostrum just below and behind the mandible, the other in the cuticle just above and 

 behind the mandible. 



From the anterior end of the endosternite a fasciculus of strong muscles runs to and is 

 inserted in the lower posterior edge of the rostrum near the median line. 



Perpendicular Muscles. — I was able to distingviish eight fasciculi of dorso-ventral 

 muscles, all strongish, viz. : — 



1. A fasciculus arising from the dorsal cuticle in front of the reniform and pericibal 

 salivary glands, and not very far from the median line of the body ; this bundle is 

 inclined slightly forward, and is inserted in the hind edge of the rostrum. 



2. A fasciculus arising from the same place, but passing almost perpendicularly down- 

 ward and inserted into the ventral cuticle. 



