Gatty Marine Lahorniory, St. Andrexos. 239 



frequently in the vessels and sinuses. Tliere is a mixture of 

 venous and arterial blood in the braneliire. The author 

 does not touch on the structure of the nervous system of 

 Oivenia, the topography of the alimentary ca»iai, the hypo- 

 dermic canals of the sixth seoment, and other features subse- 

 quently to be described, and his main points are liistological. 

 The illustrations are ciiicfly in outline. 



Ko trace of a central nervous system is observed in 

 Owenia fusiformis till the folds of the month are cut in the 

 transverse sections*, and the fir^t definite aj)pearance of a 

 layer similar to nerve-tissue is the presence of a pale band 

 external to the stained basement-layer of the inner border 

 of a lateral flap of the mouth. It resembles a differentiated 

 stripe of hypoderm from which cells and pigment are absent, 

 but the fine stride are continued through it to the basement- 

 tis.sue, the whole being minutely fibrillar like the nerve- 

 tissue, and generally dotted with minute grannies. It. fades 

 away before reaching the free or ventral edge of the lateral 

 Hap, and disappears similarly at the dorsal edge of the fold. 

 Then (for it is difficult to cut exactly on the same level) a 

 corresponding band appears on the opposite labial fold. 

 This pale belt is considered by some, e. y., Ziircher, to be 

 basement-tissue, but it seems to be somewhat ditf'erent. In 

 any case, the contrast between it and the condition, for 

 instance, in the proboscis of the armed Nemertean with its 

 large strands of nerves and their reticulations is marked, yet 



* Whilst many advautafres are pained by the use of paraffin, cellu- 

 loidiiie, and other substances for imbedding, the old plan of fine sections 

 made directly from careiully prepared spirit-specimens is not without 

 value in checking' tlie proportional tliickness of the muscular layers and 

 other parts. Thus, in the case of Oivenia the great thickness of the 

 longitudinal muscles of the body-wall can only be appreciated in this 

 way, and so with the proportional size of the mucous glands and the 

 tough nature of the basement-layer. In such preparations more than 

 forty years old the delicacy of the hypodermic ^ layer has caused most of 

 it to be removed in the manipulations before and after preservation, but 

 in every case the nerve-cord iirmly adheres to the basement-tissue in the 

 mid-ventral line, thus demonstrating its comparatively tough nature in 

 contrast with the hypoderm. In such sections the gut tills the entire 

 area, with the exception of the mucous glands, though, of course, in life 

 the coelomic space was larger. The term hypoderm in the structure of 

 the I'olychseta refers to the glandular and granular layer, often areolaled, 

 beneath the cuticle. It is an ectodermic structure. 



* I am indebted to Mr. E. W. Shnnn, B.Sc, now Captain in the 

 Northumberland Fusiliers, Mr. J. W. Pryde, M.A., now Lieutenant in 

 the Black Watch, and to Miss Harvey, of Edinburgh, for aid in making 

 the various section?. 



