322 Mil. W. B. S. BENHAM ON THE MUSCULAR 



this Memoir was in type ; the reader is referred to his paper in Quart. Journ. Micr. 

 Sci., Jan. 1884. 



2. Mesosomatic Entochondntes. — There are six of these, lying on the floor of the 

 raesosoma on the hinder border of the bases of the appendages (see PI. LXXII. for 

 their position). The nerve-cord is dorsal to these entochondrites, and not below them 

 as it is in the case of the plastron. They are more or less rectangular in shape, with 

 their long axis transversely directed (PI. LXXVT. fig. 8). The anterior and posterior 

 comers are slightly produced, giving attachment to muscles. On the median ventral 

 surface is a ridge. 



These have the same microscopic structure as the plastron. 



V. The Entapo^hyses. 



There are seven pairs of these, one on the thoracic carapace on its hinder vertical 

 border, the rest in a line with these on the abdominal carapace. Each consists of an 

 invagination of the chitin to form a strong process, directed forwards, downwards, and 

 slightly inwards ; they are flattened from side to side. Several muscles are attached to 

 each entapophysis ; thus, e. (j., on the inner face, anteriorly, are attached the bundles of 

 the oblique muscle (1, 2, 3); posteriorly, in the case of the last three, the ventral pygo- 

 tergal (9) ; to the ventral edge, the posterior lamellar muscle (23) from the abdominal 

 appendage of the same segment ; on the outer surface, ventrally, the posterior lamellar 

 muscle (22) from the succeeding abdominal appendage; posteriorly, the dorsal pygal 

 muscle (G). To difi'erent entapophyscs are attached different muscles. 



To the outer edge of each entapophysis is attached a half-ring of hyaline cartilage 

 (capsuligenous tissue of Lankester) by the intervention of some fibro-cartilage (fibro- 

 massive tissue of Lankester) ; by means of this ring some of the muscles from the 

 abdominal appendages are attached. 



The fibro-massive tissue is continuous from each entapophysis to the next one, and 

 forms a definite band-like structure on each side of the mesosoma, to which I give the 

 name of " entapophysial ligament " (PI. LXXIII. ec) : it ends in the postabdominal 

 sternite. 



Microscopic Structure. — The entapophyses are similar to the carapace ; the outermost 

 layer of chitinin the latter now, of course, lines the cavity which exists within the 

 entapophysis: the layers are a good deal contorted, and are pierced by tubes in the 

 same way as is the carapace. Some of these carry hairs, which project within the 

 cavity. 



Below the chitin are seen the epidermic cells which produce the chitin. These are 

 a good deal obscured by pigment. 



