328 Ww. A. HASWELI 
(1) that the annular bands run throughout in the intervals 
between the radial muscle-columns; (2) that the annular 
bands perforate the muscle-columns throughout ; and (3) that 
the same arrangement as in (2) holds good except in the neigh- 
bourhood of the raphes, where the annular rings pass to the 
position they occupy throughout in (1)." 
The lumen of the proventriculus may be deseribed as 
a vertical slit the upper and lower ends of which he near the 
dorsal and ventral raphes respectively. This is the form 
assumed in the contracted state ; in complete contraction the 
sides of the slit are in close contact: when dilated the slit 
expands till in transverse section its outline becomes ellipsoidal. 
The thick wall of the proventriculus (Pl. 15, fig. 1) consists 
of the following layers: (1) splanchnic layer of coelomic 
epithelium ; (2) outer fibrous membrane ; (3) layer of radial 
musele-columns and annular muscle-bands; (4) mner fibrous 
membrane ; (5) enteric epithelium ; (6) cuticle. 
The coelomic layer is a very thin one, recognizable by its 
infrequent flattened nuclei.” The outer fibrous membrane 1s 
the layer described by Malaquin, and earher by myself, as 
a layer of non-striated muscle. Of its contractile character 
I am by no means certain. It is a thin layer, only about 
(0-003 mm. in thickness in the largest forms, and is made up of 
two strata in the outer of which the fibres run transversely 
and in the inner longitudinally: the fibres are exceedingly 
fine and there are no nuclei. The chief function of this layer 
seems to be to serve for the insertion of the radial fibres and the 
fibres of the annular bands. ‘The imner fibrous membrane is 
a similar layer, also composed of outer transverse and mner 
longitudinal fibres: it has the inner ends of the radial fibres 
inserted into it. At the raphes paired trabeculae pass at regular 
intervals from the inner fibrous membrane to the outer and bind 
the two layers firmly together. 
The enteric epithelium and the cuticle need not be specially 
1 Towards the anterior end of the proventriculus the regularity of the 
rings on the surface is broken owing to a modification in the arrangement 
of the radial muscles associated with the presence of the chitinous plates. 
