170 MR W. E. HOYLE ON 



1. Transverse fibres, immediately underlying the epidermis. 



2. Longitudinal fibres, arranged in bundles, lying for the most part imme- 



diately below the coelomic epithelium. 



3. Oblique fibres, placed obliquely, however, both to the dorso-ventral 



plane of the body and to planes cutting it transversely. 



1. The Transverse Layer of muscular fibres is very thin, it being only one 

 fibre thick ; in some cases there seemed to be two or even three such layers, 

 but this appearance was probably owing to a slight obliquity of those particular 

 sections. 



It is situated immediately within the epithelium, so that its fibres are for 

 the most part parallel to- the cuticle, and they lie in planes which are approxi- 

 mately transverse to the body of the animal. 



The appearance of this sheet of fibres is seen in PL XXVII. fig. 14 ; the 

 fibres branch dichotomously, and at intervals unite with each other so as to 

 form a fine network with elongated meshes, in which the cells of the parenchyma 

 of the body- wall may be noticed. 



In the body proper of the animal this layer is developed almost exclusively 

 on the sides, its fibres not often crossing the ventral, and hardly ever the dorsal 

 median line. 



In one specimen about 1 mm. from the caudal extremity, I noticed a small 

 patch of these fibres dorsally situated, but this might have been an individual 

 peculiarity. The cephalic region, however, shows a great change in the 

 arrangement of this layer, for there it is best developed on the dorsal and 

 ventral aspects of the body, and to a much smaller extent on the sides. 



With respect to the nature of the individual fibres, but little can be said. 

 They are very thin (about O'OOl mm.), and I could not detect in them that 

 transverse striation which was noticed by Leuckart.* Some of the better 

 preserved specimens showed, however, a kind of sarcolemma, an exceedingly 

 thin sheath with a well-defined outline, and with small ovoid nuclei (PI. XXVII. 

 fig. 16, nu). 



2. The Longitudinal Layer varies a good deal in its arrangement in different 

 parts of the animal, and it will be advantageous to describe it as seen at about 

 the middle of the body. A section taken in this situation is shown in PI. 

 XXVII. figs. 10 and 13, m.l), and it will be at once noticed that the longitudinal 

 muscles are situated at some distance from the external surface, being separated 

 from it by the whole thickness of the body- wall. Its fibres, moreover, are 

 grouped into definite bundles, which in the ventral region present a more or 

 less elongated oval section, while in the lateral and dorsal regions they are 



* Loc. cit., p. 40. 



