Gatty Marine Laboratory, St. Andrews. 230 



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

 venous and arterial blood in tiie branchiae. The author 

 does not touch on the structure of the nervous system oF 

 Owenia, the topography of the alimentary canal, the hypo- 

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

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

 The illustrations are chiefly in outline. 



No ti-ace of a central nervous system is observed in 

 Owenia fusifonnis till the folds of the rnouth are cut in the 

 transverse sections^, and the first definite appearance 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 wiiich cells and pigment are absent, 

 but the fine striae are continued thruugh it to the basement- 

 tissue, the whole being minutely fibrillar like the nerve- 

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

 away before reaching the free or ventral edge of the lateral 

 flap, and disap|)ears 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-tissuCj but it seems to be somewhat different. Tii 

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

 instance, in the proboscis of the armed Nemertean with its 

 large strands of nerves and their reticulations is marked, yet 



* Whilst many advaiitau-es are gained by the use of })arafHn, cellu- 

 loidine, and other suhstauces for iuibeddiuj.'-, the old plan oi' line sections 

 made directly from careiuily prepared spirit-specimens is not without 

 value in checking- the proportional thickness of the muscular layers and 

 other parts. Thus, in tJbe case of Owenia 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 basemeut-la^er. In such preparations more than 

 forty years old the delicaev 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 firmly adheres to tlie basement-tissue in tlie 

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

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

 area, wath the exception of the mucous glands, tliough, of course, in life 

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

 the Polychgeta refers to the glandular and granular layer, often areolated, 

 beneath the cuticle. It is an ectodermic structure. 



'^ I am indebted to Mr. E. W. Shann, 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 sections. 



