Oatty Marine Laboratory, St. Andrews. 37 



multitude oh' minute processes — probably of great use in 

 fixation. Another structural characteristic is that of the 

 first or collar bristles, which, for example, in the Spirorbids 

 are of specific importance. The absence of tentacles (two 

 of which are present in the Sabellids) and the presence of a 

 calcareous operculum in the Serpulidsare distinctive, just as 

 the long branchiae of the Sabellids are in contrast with the 

 shorter organs in the Serpulids. 



The secretion of the tube, as indicated under Pomatocerus 

 triqueter, takes place with considerable rapidity — for instance, 

 on the carapace of the shore-crab, on porcelain or stone- 

 vessels and bottles thrown into the sea, and is further proved 

 by observations in confinement. Mr. Arnold Watson thinks 

 it is secreted by the outer side of the collar, since, as soon as 

 the anterior part of the annelid emerges, the collar is folded 

 over the edge of its tube, its two lobes meeting over the 

 mucro. He adds, however, that the formation of a dia- 

 phragm in a broken tube shows that other parts may likewise 

 secrete the calcareous matter. As detailed in the structure 

 of the hypoderm, the collar and the free surfaces of the 

 thoracic jacket contain much glandular tissue, as likewise 

 do the lamella? or elevations for the tori uncinigeri. 



Hypoderm. — In the anterior sections of the body-wall of 

 Pomatocerus triqueter the dorsal is distinguished from the 

 ventral hypoderm by the intensity of the stain (Ehrlich's 

 Hsematoxylin and Eosin) * in the latter, viz., from the slight 

 projection below the enlarged base of the dorsal flap or pro- 

 cess to that of the opposite side, the glandular tissue, like 

 that of the oesophageal wall, readily absorbing this stain, so 

 much so as to become opaque. The dorsal hypoderm, on the 

 other hand, has only the nuclei tinted near its outer edge, and 

 the inner part of the enlarged base of the dorsal flap shows 

 likewise glandular tissue. The thoracic collar anteriorly 

 (PI. IV. fig. 21) is somewhat complex in Pomatocerus tri- 

 queter, having dorsally a large fan-shaped lamella on each 

 side, then a gap between it and the continuous ventral 

 portion, of the collar, whilst a small lamella with processes 

 on the edge occurs at the gap, its base having a closer con- 

 nection with the ventral^ than the dorsal moiety. This 

 condition of the ventral hypoderm continues backward to 

 the end of the thoracic glands, the lateral processes bearing 

 the hooks being especially glandular. Then the glandular 



* I am indebted to Miss Laniont, of the Zoological Department of 

 Edinburgh University,, for aid in section-making, my own trained men 

 being on service. 



