Gatly Marine Laboratory., St. Andreios. 243 



functions. It is interesting that Dr. Goodrich"^ found a 

 similar organ (his " muscular pad ") in Saccocirrus and 

 Protodrilus. The hody-wall at this level again presents a 

 change in its hypoderni (which throughout has a firm 

 exterior film or cuticle), since, though somewhat diminished 

 dorsally, it is now of a considerable tiiickness mid-ventrally, 

 its densest part being at the nerve-cords, which have moved 

 downward, so that they are separated by about a sixth of the 

 circumference of the body (PI. VIII. fig. 7). The oesophagus 

 has special fasciculi of muscles laterally and dorsally, besides 

 the radiating fibres. 



The next important change is the merging of the oesopha- 

 geal region of the canal, with its boldly arranged coat con- 

 tinuous with the external hypoderm, into the stomachal 

 region at the third septum, with its granular glandular 

 surface (PI. VIII. fig. 7) and its external muscular coat, the 

 wiiole internal surface of the stomach being by-and-by thus 

 transformed. 



At the couimencement of this region of the gut at the 

 third septum a complex muscular sheath connected with 

 the lip-organ occurs ventrally, with thickened muscular 

 pillars at each side — abutting on a membranous space to 

 the exterior and just over the nerve-trunks, certain of the 

 fibres, moreover, a little further back being attached to the 

 basement-tissue over the outer part of the nerve-cords. 

 Blood-vessels occur in the large space which is thus soon 

 formed below the alimentary canal, and the vessel in the 

 median mesentery (which is attached to the upper border of 

 the mass of muscle stretching from side to side over the area 

 above the nerve-cords — a little behind the section figured in 

 PI. VIII. fig. 7) is distinct, the special mesenteric area still 

 being visible externally, though much reduced in size. 

 Between the basement-tissue of the body-wall and this trans- 

 verse muscular mass lie the ventral longitudinal muscles 

 [vmS). The great cavity appears to contain coelomic fluid 

 and corpuscles, and is shut off by a shelf of septal tissue 

 (PI. VIII. fig. 7, bt.) continuous at each side with that of 

 the body-wall, whilst the upper area on each side of the 

 alimentary canal is occupied by elastic connective-tissue 

 strands and by the muscular fasciculi along the dorsal wall 

 of the canal. The body-wall at this region has dorsally the 

 longitudinal muscles {dm.), which may be held to cease at 

 the junction of the transverse platform of septal tissue a 

 little below the middle, of longitudinal muscular fibres 



* Quail. Jouni, Micr. Sci. ii. ,<., vol. ,\liv. p. 415, sections 18 >.^- 20. 



, 



