258 Prof. M'lntosh's Notes from the 



ventral mesenteries separate the muscles of the sides, but 

 there is little to distinguish between the areas of the dorsal 

 and the ventral muscles respectively. 



Proceeding backward the epithelium of the gut becomes 

 somewhat finer, the longiiudinal muscles form a uniform 

 layer all round without evident differentiation other than 

 the attachment of the median mesenteries, and the hypoderm 

 still remains thicker ventrally, whilst the blood-vessels and. 

 ova show no change. A gelatinoid (])rotoplasmic) layer 

 envelops the longitudinal muscles internally, the repre- 

 sentative of the coelomic epithelial layer. 



Then the intestine in section shows a keel ventrally, and 

 septal strands, apparently muscular, pass from it to the 

 body-wall, making membranous (and partly muscular) septa 

 to the latter, viz., one on each side of the gut. These septa, 

 however, soon reach the dorsal region and become attached 

 to a process from the dorsal wall of the gut on each side, 

 the dilated (globular) region of the canal being tilled with 

 food below these, the ventral portion forming a solid apex. 

 The septa tend to mount upward on the interior of the 

 body- wall, leaving two great areas ventrally on each side of 

 the canal and a narrow dorsal chamber above the septa. 

 Finally, the septum disappears, leaving only a small vessel 

 at the dorsal mesentery. Then a sinus again forms on the 

 upper wall of the gut, the ova continue as in front, and 

 the section of the nerve-cord is more or less circular. 



Behind the former region the body-wall becomes somewhat 

 thinner, the thickest region of the areolated hypoderm being 

 the ventral. The nerve-area is comparatively large and ovoid. 

 The basement-layer and, it may be, fine circular fibres occur 

 internally, whilst the longitudinal muscular fibres are only 

 differentiated by the median mesenteries dorsally and ven- 

 trally. The gut is large, with a firm external wall and a 

 single layer of cylindrical epithelium, the nuclei being 

 symmetrically arranged in the middle. No dorsal vessel 

 is visible, but the Mlled external wall of a sinus occurs 

 laterally on the intestine. The ventral blood-vessel is large 

 and the mesentery leading to the ventral wall is loaded on 

 each side with developing ova, the larger forms distending 

 the coelomic cavity on each side (PI. IX. fig. 31). 



The tip of the tail is bilobed, with, in addition, a ventral 

 median semicircular lobe, and is richly ciliated (PI. X. fig. 32), 

 a short terminal portion of the intestine being straight, the 

 next (in front) being indicated by a slight constriction, whilst 

 the third is almost elliptical, from marked constrictions 

 in front and rear. In most cases, when removed from the 



