SPECIES OF THE GENUS AULODRILUS. 951 



sliown by the prostate and the atrium in these worms, as we shall 

 see later. That the epitlielial cells of the setal sac, filled with 

 secretion generally lose their cellular structure, except in the 

 small ventral portion, which is continuous externally with the 

 outer tubular part of the sac and not being connected with the 

 glandular cells is hence devoid of secretion, can be easily followed 

 in sections. 



Each glandular mass consists of a number of somewhat elon- 

 gated pear-shaped cells closely pressed together. The cells have 

 a frothy appearance on account of the secretion they are filled 

 with, have mostly lost their cellular outlines, are deeply stained 

 with hsematoxylin or similar stains, and are similar to those of 

 the prostate ; only a few nuclei are present and all this tends 

 to show that after secreting they lose their structure. 



The septa are thin throughout the body. The first septum 

 lies between the third and fourth segments. 



Alimentary canal. — The buccal cavity is capable of extrusion ; 

 the epithelial cells lining it are devoid of cilia. The pharynx 

 occupies segments 2 and 3, and is covered over by a small amount 

 of chlorogogen pigment ; its wall is folded so that about 3-4 

 diverticula which may be again divided into two arise from it ; 

 in one case a fairly long diverticulum arising from the anterior 

 part ran independently for some distance and then opened into 

 its posterior part. The pharyngeal epithelium is composed of 

 high columnar cells with nuclei about the middle of their length, 

 and provided with cilia of large size, Avhich arising from the 

 opposite walls meet in the somewhat narrow lumen of some of 

 the diverticula. In a few specimens having a more slender body 

 the pharynx was not folded, but here the cells of the dorsal wall, 

 about 45-70 /a in height formed a sort of disc-like structure pro- 

 jecting into the phaiyngeal cavity, which consequently appeared 

 of a somewhat crescentic form. The cells lining the ventral 

 portion of the wall here were only 27-36 fx in height and 4'5 fx in 

 breadth. Outside the pharyngeal epithelium lies a fine layer of 

 cii-cular muscle fibres, from which fine strands of muscles arise 

 here and there, specially on the dorsal and lateral sides and 

 connect it with the body-wall. 



The pharyngeal gland cells lie in groups separated by the 

 muscle strands, which form a sort of loose network around them 

 and largely fill up the body-cavity of the pharyngeal region. Each 

 gland cell takes a deeper hasmatoxylin stain than the rest of the 

 tissues ; it consists of a broad outer expanded portion in which 

 lies the nucleus with the nucleolus and a long inner narrow 

 portion, which can be easily mistaken for a connective tissue or a 

 fine muscle fibre. The cell groups surround each of the pharyn- 

 geal diverticula referred to before. In sections most of the gland 

 cells are cut in such a way that their long inner stalks become 

 completely separated off from their outer expanded portions and 

 look like fibres. Hence arises a difficulty in tracing the cells to 

 their inner ends. That the fine stalks of the gland cells reach 



64* 



