136 A. RICHARDS. 



the parenchyma tissue is made up of loose intercellular material 

 (of cellular or'gin, of course). Thus a cell consists of a nucleus 

 and its attendant cytoplasm supported by a large mass of inter- 

 cellular material. Usually the cells are somewhat distant from 

 each other. Should two or more of them come to lie closely side 

 by side, it is conceivable that their cytoplasmic masses might 

 easily fuse and a true syncytium be formed. It will be seen 

 that this is a possible explanation of binucleate parenchyma cells 

 where such occur (Fig. 2). The cellular character of the primary 

 anlage is similar to that of the parenchyma, although, of course, 

 the anlage has very little intercellular material and many cells. 



Child describes the testes as arising from visibly differentiated 

 muscle cells; he did not, however, observe that muscle cells take 

 part in the formation of the ovary, "probably because these cells 

 do not occur in the region where the ovaries develop" (Child, 

 '06). Muscle cells certainly do occur in the region of the 

 ovaries 1 but I have never seen any evidence that they take 

 any part whatever in the development of the female germ cells. 



Since the primary anlage arises from a parenchyma which has 

 no visible differentiation there would seem to be no visible basis 

 for a continuity of germ plasm here. The expression "primordial 

 germ cell" has little meaning therefore when applied to a cestode 

 for there is no apparent difference, except of position, 2 in the 

 cells which will go to form the ova and those which will form the 



v 



vitellaria or the walls of the ducts. 



The primary anlage grows both outward toward the edge of 

 the proglottid and inward toward the ventral surface. Its out- 

 ward growth is in the form of a cord of cells being extended to 

 the exterior. Before the solid cord reaches the exterior its middle 

 portion becomes hollowed out to form a lumen. This lumen 

 subsequently develops a cuticle which to all appearances is just 

 like that on the surface of the body. This outw r ard growth 

 becomes the vagina and the receptaculum seminis. Its develop- 



'See photomicrographs for circular and longitudinal layers; scattered fibers 

 also occur. 



2 This difference of position, however, is a very constant one. The cells from which 

 the ova develop are early marked off by their position and never take part in any 

 other development. The facts are not opposed to the continuity theory; they simply 

 afford no evidence for it. 



