PLATYHELMIA. 33 



A gland is an organ essentially composed of one or more epithelial-cells, 

 in which some special secretion or excretion is formed. The simple uni- 

 cellular, i.e., one-celled, condition is seen in the accessory glands. 



The vesicula seminalis, ejaculatory duct, accessory glands, and 

 penis are contained in the cirrus-sac (cr.s), a hollow oval body 

 with muscular walls, lying between the ventral sucker and genital 

 opening. 



(2) The Female Organs are made up of the following parts: 

 The unpaired ovary (Dr) lies on the right side, in front of the 

 spermaries. It is composed of several branched tubes, which 

 unite together to form the oviduct (Ov). This is at first very 

 narrow, then gradually enlarges and becomes considerably con- 

 voluted, and finally narrowing, opens by the female aperture 

 (Fig. 6, B, odf). The dilated part of the oviduct (uterus) is 

 generally found full of eggs, in which embryos are beginning to 

 develop. Two glands are connected with the female organs. 

 (1) The yolk-glands (Do), which secrete a nutritive substance 

 (yolk) for the use of the developing embryos, are paired, and 

 each of them is made up of an immense number of minute 

 rounded bodies (acini) of glandular nature, and extends over a 

 lateral strip outside the other reproductive organs. Behind the 

 spermaries the two meet in the middle line. From the acini fine 

 ducts proceed, which unite into larger ones that finally open into 

 a longitudinal duct which runs along the inner side of the gland. 

 Just in front of the anterior spermary a transverse duct arises 

 from this trunk, which unites with its fellow in the middle line 

 to form a small yolk-reservoir, from which the short impaired yolk- 

 dud runs forwards to join the oviduct not far from its commence- 

 ment. Just before their union a fine tube, the vagina (Laurer's 

 canal), through which sperms are introduced into the oviduct, 

 passes to the yolk-duct from the dorsal surface, where it opens 

 by a minute aperture. (2) The shell-gland, by which the egg- 

 shells are secreted, is similar in structure to the accessory gland. 

 It is a rounded mass, the elements of which open into the 

 oviduct near its junction with the yolk-duct. (See Fig. 7, just 

 below convoluted oviduct.) 



Histology. The tubules of the spermary are supported by a 



structureless wall, on the outside of which filamentous contractile 



cells are arranged longitudinally. There appears to be a lining 



of germinal epithelial cells, sperm-mother-cells, some of which 



2 3 



