47 



The leeches are not all uniform in this respect, but the 

 number of spots is always 4, 6, or 8, and the first annulus 

 always has at least four large spots. In that part of the 

 anterior sucker where one would expect to find eyes are 

 large black spots, which I consider to be merely pigment- cells. 

 There are eight or nine of these, at irregular distances 

 apart ; and some so nearly touch as to appear to the unaided 

 eye to coalesce. 



Bod// Wall. — The epidermis consists of a layer of cells 

 elongated in a direction at right angles to the axis of the 

 body, covered with a cuticle secreted at the free edge and 

 having their nuclei away from their external border. Among 

 the epidermal cells are epithelial glands for the secretion 

 of mucus. The derma consists of a thick layer of connective 

 tissue, which includes very small fibre-forming cells. Deep 

 down in the derma are large flattened cells about 40 \l in 

 length, and half as thick, situated immediately outside the 

 muscle layer. They are far more numerous in the gills, 

 whose structure resembles that of the body wall, as far as 

 epidermis and derma are concerned (text figs. 4b and 5). 

 The muscle layers run below the connective tissue layer, and 

 immediately below them are found the cocoon-gland . cells, 

 which, however, do not attain the huge dimensions of those 

 found in Calliobdella, Abranchus, and Platybdella, being only 

 about 50 ju, in their greatest diameter, a comparatively small 

 size for such cells. Their appearance is precisely the same 

 as I have described for Platybdella (1916). Below these cells 

 run the cocoon-gland-cell ducts, interspersed with the longi- 

 tudinal muscle fibres. There are no yellowish-brown pigment 

 cells, such as are seen in Calliobdella (1914). The muscle is 

 not striped, and the cells are about 1 mm. in length by 

 80-100 /x in breadth. Perez and Gendre (1904a) have drawn 

 attention to some diagonal fibres in B. torpedinis, which are 

 also present in B. australis in the same region, near the 

 posterior sucker, and are intermediate between the ordinary 

 muscle cells and the type well known in . Nematodes. No 

 pigment cells are shown in the figures, but it should be 

 remembered that the leech sectioned had been decolourized 

 by preservation in alcohol. Nevertheless, sections show 

 pigment cells in the suckers. 



Coelom. — The body cavity is divided into the five 

 following regions : — A ventral sinus, a dorsal sinus, two 

 lateral sinuses, and, in parts, an intestinal sinus. The 

 dorsal blood-vessel is double, and is situated in the dorsal 

 sinus, but comes outside it occasionally, and more frequently 

 than in Pontobdella. In the more specialized genera — e.g. y 

 Calliobdella — it remains within the sinus throughout its 



