THE ANATOMY. SPERMIDUCAL GLANDS 109 



non-glandular epithelium and has thick muscular walls ; it is these which give the 

 'nacreous' appearance already referred to; the glandular part of the tube is of 

 greater calibre, and has an opaque white colour, and a rough exterior contrasting 

 with the smooth external walls of the proximal part of the tube. This glandular 

 section of the tube consists of two distinct layers of cells. The innermost coat is 

 formed of a layer of not very deep columnar cells, often loaded with granules; 

 below these are several layers, forming a stratum of considerable thickness, of pear- 

 shaped cells with long processes, which penetrate between the columnar cells and 

 therefore abut upon the lumen, being thus in a position to pour their contents 

 directly into the lumen ; the entire structure of the lining epithelium is in fact very 

 suggestive of that of the clitellum ; there is the same specialization of its epithelium 

 into two sorts of cells. Outside the epithelium is the peritoneal membrane. This 

 kind of gland is found not only in the genus Acanthodrilus, but also in very nearly 

 all the members of the family Acanthodrilidae ; it also occurs in such Cryptodrilidae 

 as have a tubular gland of a similar form to that of the Acanthodrilidae, with a few 

 exceptions to be referred to, and finally in a few Perichaetidae. There are hardly 

 even differencies of the minutest character whicli distinguish the gland in these 

 various types ; sometimes the innermost epithelium is more plainly columnar and 

 not so glandular as has been described ; but this is very possibly merely a matter 

 of more or less activity in the secreting processes. Ocnerodrilus (including a few 

 allied genera which I group together near this) and Kerria are the only exceptions, 

 among the Megascolicidae which have a gland of a tubular form, to the description 

 just given; in these genera the difference is in the fact that the lining of the entire 

 tube is formed by a single layer of cells only. 



The second form of the spermiducal gland seen in the Megascolicidae characterizes 

 the Perichaetidae and is to be found in a large number of Cryptodrilidae ; it occurs 

 only in one Acanthodrilid. Here we have first of all the same differentiation of the 

 gland into a glandular and a non-glandular portion ; the external duct is the non- 

 glandular part and its length varies much in different species ; certain species of 

 Perickaeta, for example, are characterized by this duct being curved into a horseshoe- 

 shape, and diminishing in calibre towards its external aperture ; in others, on the 

 contrary, it is short and straight ; in none is it absent ; it is, as in the case of the 

 gland of the first kind, muscular, with a lining of columnar cells. In these worms 

 the glandular part does not form a comparatively narrow tube of equal calibre 

 throughout ; it has the appearance of a racemose gland much divided up into lobules ; 

 the lobulation is sometimes so pronounced as to produce a very loose texture of the 

 gland ; sometimes the organ is more compact ; it is also sometimes larger and some- 



