38 Prof. M'Intosh's Notes from the 



tissue forms a patch on each side of the middle line ventrally, 

 as well as on the edges of the ventro-lateral processes, and 

 thus these form a contrast with the dorsal (branchial) pro- 

 cesses. Thereafter (proceeding backward) the glandular 

 tissue is almost absent from the median ventral region, but 

 is highly developed on the ventro-lateral processes ; soon, 

 however, it again appears in the ventral plate or fillet, which 

 has glands along its lower edge, a few remaining in the 

 hypoderm of the ventral surface of the body- wall. 



So long as the free flap of the thoracic jacket or collar 

 occurs, the glandular tissue in the hypoderm of the ventral 

 edge of the flap is dotted at intervals with glands, and they 

 are also distributed along the ventral hypoderm of the 

 body- wall, but in moderate numbers. As the flap diminishes 

 the ventral median groove of the body-wall becomes deeper, 

 but its hypoderm is thinner than that at the sides (beneath 

 the ventral longitudinal muscles), the glands, however, being 

 continued in it. When the jacket ends, the hypoderm 

 generally is somewhat thinner, the ventral groove rather 

 more shallow, and the glands are but slightly developed, the 

 most conspicuous aggregations being in the lateral thickenings 

 bearing the hooks, so that the region is in marked contrast 

 with the anterior. This description applies to the body-wall 

 as far backward as the valvular region of the alimentary 

 canal. 



In the posterior division of the body the glands still occur 

 in the lateral region and on the lamellae for the hooks, as 

 well as a few along the ventral border, especially on each 

 side of the ventral groove. Very few occur dorsally — indeed, 

 in most sections they are absent form the dorsal arch, only 

 nuclei occurring there. 



The hypoderm at the level of the origin of the opercular 

 stalk (PI. IV. fig. 20) often presents a fan-like arrangement 

 of its long cells, as at hpe., a condition probably due to 

 slight folds iu the sections, but such recalls the aspect of some 

 simple sense-organs, e. g. eyes, though no pigment is present, 

 only the stout basement-tissue on which the cells rest. 

 That this modified hypoderm in the anterior region performs 

 special functions is evident by contrasting the outer and 

 inner surfaces of the thoracic collar or jacket, also by the 

 massive thickness of some parts, the thinness of others, and 

 the blanks in the layer only invested by cuticle (Jib.) in the 

 same figure. The almost perfect regularity of the nuclei 

 and the fibroid aspect of the long cells are other features of 

 moment. The blanks (lib.) in the hypodermic coating 

 consist of a reticulum of nucleated cells supported internally 



