432 Prof. M'lntosh on (lie 



and is wholly ventral, though with the same immediate 

 relations, viz., the external (now ventral) chitinous layer, 

 nnd internally the fibres of the oblique muscle. In the 

 fresh specimen the rapid diminution and increase of each 

 muscle and the perfect continuity of the fibres are well 

 shown. Thereafter it rapidly enlarges and approaches the 

 middle line, assuming an ovoid form in transverse section — 

 the deepest fasciculi being in the middle. On attaining full 

 development in the posterior region, the size exceeds that of 

 the dorsal, the fasciculi slanting from the summit of the 

 nerve near the median line outward to the attachment of the 

 external vertical muscle. The outline in the preparations 

 (transverse sections) is convex inferiorly — an approach to 

 the condition observed at the commencement of the anterior 

 region of the body. It still has a very thin chitinous in- 

 vestment externally, and the oblique muscle bounds it 

 internally, except the ova distend the body-wall and separate 

 them. Toward the tip of the tail a considerable diminution 

 takes place before its termination. 



In the ordinary condition of the snout, as well as during 

 the development of the peculiar organs on the sides of the 

 body, a granular fluid is observed oscillating (under com- 

 pression) in the interior of both cephalic muscles (median 

 and lateral) . The detached globules (which roll about) 

 seem to be associated especially with the changes and altered 

 nutrition of the reproductive period, and occur throughout 

 the whole extent of the muscular cavity. 



After the separation of the central muscles of the snout 

 the conspicuous hypodermic fibres already described occur 

 in both dorsal and ventral regions. Such are probably 

 elastic, and are connected functionally with the great central 

 vascular region. They form a somewhat radiate arrange- 

 ment around the ventral space inferiorly. Posterior to the 

 fibres just mentioned are a series of muscular fibres, which 

 subdivide the great vascular area — wide in the middle and 

 narrow at the ends in transverse section. They form a 

 powerful transverse muscle connecting the inferior ends of 

 the external chitinous septa (between the central and 

 external muscles) and the inferior borders of the former 

 area. The space is further divided by a series of strong- 

 fibres which pass from the centre and sides of the roof 

 downward to the ventral chamber, where they spread out, 

 forming intersecting bands. As the central muscle of the 

 snout rapidly disappears in this region, the transverse 

 muscular plate is attached at each side to the somewhat 

 anofular inner border of the chitinous investment of the 



■*! 



