34 Prof. M'Intosh's Notes from the 



from the alimentary canal to the mid-dorsal groove, and 

 they by-and-by separate the nervous masses on each side. 

 A projecting process, probably glandular, occurs on each 

 side of the middle line ventrally, and the hypoderm is 

 specially thickened toward its exterior. At the outer edge 

 of the space lying below and external to the great dorsal 

 muscle on each side is a muscular band, but such is distinct 

 from the ventral longitudinal muscles which in section 

 appear as small rounded areas on each side of the middle 

 line, and with the nerve-trunks and the great neural canals 

 at their inner borders. Proceeding backward the ventral 

 longitudinal muscles gradually separate from each other and 

 become flattened in section, thus carrying the nerve-trunks 

 further from the middle line, the ventral blood-vessel lying 

 in the centre with the alimentary canal above it grasped 

 between the massive dorsal longitudinal muscles. In the 

 long space between the ventral muscles and the nerve-cords 

 are several small fascicules of longitudinal muscular fibres, 

 and large processes of the alimentary canal appear above 

 the inner edges of the ventral longitudinal muscles. The 

 vascularity of the inner region of the hypoderm is note- 

 worthy. Further backward thcoesophageal region diminishes, 

 whilst a process of the gut appears above it, and the two 

 processes beneath the oesophageal chamber have moved 

 inward toward the ventral blood-vessel, whilst the dorsal 

 longitudinal muscles are somewhat further apart. The 

 ventral longitudinal muscles are larger and are elongate- 

 ovoid in transverse section with the nerve-cords at their 

 inner edges. They are separated by the processes of the 

 gut and the ventral blood-vessel. 



In the posterior region a change has taken place in the 

 structure of the body-wall. The dorsal longitudinal muscles 

 have now spread out into thick plates on each side of the 

 middle line, and in the lateral region end in a massive 

 rounded area of folded muscular fasciculi, which in section 

 show a pennate or feathered aspect. A large alimentary 

 canal occupies the centre. The ventral longitudinal muscles 

 are still proportionally small, forming, in section, elongated 

 plates somewhat thicker externally, and with the nerve- 

 cords and their large neural canals at the inner edge. They 

 are separated from each other by the ventral blood-vessel, 

 which is in contact with the gut superiorly. The inner 

 edges of the ventral muscles have thus moved nearer the 

 middle line. The ventral hypoderm now presents the same 

 structure as the dorsal. 



The hypoderm in Serpula vermicularis is firmer than in 



