278 Platybdella Anarrhichae 
a blood vessel), two lateral sinuses, and, in parts, an intestinal sinus, as 
shown in Fig. 4. 
Body Wall. The epidermis consists of a layer of cells elongated 
in a direction at right angles to the long axis of the body, having their 
nuclei away from the external border, and a cuticle secreted at the free 
edge. The derma is rich in large flattened cells 40 a in length and half 
as thick, which however are unlike those of Abranchus in being situated 
immediately outside the muscle layer, where they form a continuous 
layer. Their nuclei are very large and flattened in the same manner 
and direction as the cells, 20 x 10 p, in diameter. Outside this cell 
layer is a thick layer of connective tissue which includes very small 
Fig. 2. Platybdella anarrhichae. Transverse section of the body wall much magnified. 
cut. cuticle; ep. epidermis; conn, tiss. connective tissue; fibr.l. fibrous cell layer; 
d.c. large subdermal cells, in this case not pigment cells; m.l. muscle layer (c. circular; 
ob. oblique; long, longitudinal); c.g.c. cocoon gland cell. 
fibre-forming cells (Fig. 2). Pigment cells do not occur, but the above- 
mentioned large cells occupy the place and position of the large pigment 
cells which occur in Calliobdella and other genera, and possibly, even 
probably, are homologous with them. Platybdella differs from Abranchus 
in that in the latter genus these large cells take up practically the whole 
space between the muscle layer and the epidermis, so that the connective 
tissue layer is naturally suppressed. A striking feature of this leech is 
the cocoon gland cells situated beneath the muscle layer. They are 
of even greater size than the dermal cells already mentioned. They 
shine through the layers of the body wall in a whole specimen, unstained, 
but mounted in balsam, appearing as glistening white objects. 
