Galhj Marine Lahoratory, St. Andreios. 247 



vertical diameter, forming a long flattened organ extending 

 from the dorsal to tlie ventral region in section, and the 

 cellular lining is thrown into rugae. Both dorsal and ventral 

 short me?ienteries are double, and the wall of the dorsal 

 vessel is more muscular. The gut has the same vascular 

 investment as just mentioned, and the vessels lie outside the 

 mesentery just alluded to. At the next bristle- bundle a 

 pore similar to the first gives issue to the secretion of the 

 second pair of glandular tubes. The ventral longitudinal 

 muscles retain their more massive outline. 



After an interval the body (Pi. IX. fig, 13) increases in bulk 

 proportionally, but the hypoderm becomes thinner all round, 

 the thitkest part being that situated ventrally on each side of 

 the nerve-cords. The ventral longitudinal muscles pass far 

 upward, and encroach on the dorsal, which occupy only the 

 upper arch of the body, and each pair has a distinct median 

 notch into which the mesentery tits, the ventral mesentery 

 having the ovaries or spermaries attached to it laterally, 

 and the contents of which are shed into the coelom. Two 

 mucous glands in section occupy the upper half of the 

 coelom on each side, and the nuclei of the cells forming their 

 walls are regularly arranged. The gut stretches nearly from 

 dorsal to ventral arch, held in position by the median 

 mesenteries and also by the septa at intervals. The double 

 attachment superiorly forms a blood-channel, which com- 

 municates with a sinus [sin.) surrounding the gut, so that 

 here, instead of the isolated though reticulated vessels, there 

 is a continuous blood-channel — a development in all proba- 

 bility attained only in the adult or nearly adult condition. 

 The nerve-cord still has numerous hypodermic fibres passing 

 from the outer to the inner (ventral to dorsal) or vice versa, 

 and, in addition, fine reticulations and granules, some of 

 which are probably nuclei. Usually a slight ventral furrow 

 and a median peak dorsally indicate the double nature of the 

 area. The second pair of glandular tubes is situated to the 

 exterior of the first pair in transverse sections. 



The sixth segment is distinguished by the presence of 

 Gilson's epidermal tubes, Avliich stretch from the septum 

 between the sixth and seventh segments to that in front. 

 They are readily recognized by their position in transverse 

 sections, viz., dorsad of the groove (Gilsou's " gouttiere de 

 la sole ^^) which runs along the dorso-lateral region. They 

 are canals of considerable size, and are separated from the 

 basement-layer by a stratum of cells, the cavity in section 

 beiug also bounded externally by an arch of hypodermic 

 cells. Gilson supposed that these hypodermic canals served 



