22 



THE TURDELLARIA 



paired structure. Later, one part of this gland came to give rise 

 to germ cells, whilst the rest of it gives rise to cells similar in 

 origin, but loaded with yolk spherules. When the egg cells are 

 laid they are surrounded by these yolk or vitelline cells, upon 

 which the young embryo will feed; such a gland, forming the 

 two kinds of cells in different parts, is sometimes called a " germ- 

 vitellarium " (Fig. III. 3). We find one or a pair of such organs 



rn 



FIG. VIII. 



Plans of structure of RhalKk>coHids (from v. Graff). Left-hand figure is an Aooelous, 

 the middle is a Rhabdocoelons, and the right-hand is an Alloiocoelous Turbellarian. l; bursa 

 oopnlatrix ; en, cerebral ganglion; e, eye; g, germarium ; i, enteron ; In, ventral nerve cord ; 

 1, month ; ot, otocyst ; ov, ovary ; p, digesting parenchyma ; ph, pharynx ; rs, spennatheca ; 

 ., salivary gland ; t, testis ; u, uterus, containing an egg ; v, vitellarium ; t*, seminal vesicle ; 

 <J, chitiuous penis ; <J 9, genital pore. 



amongst the Rhabdocoelida. Further, this differentiation of 

 function may become so complete that the yolk-forming part 

 becomes entirely separated from the germ-forming region, so that 

 a "vitellarium" becomes distinguishable from a "germarium" 

 (Fig. VIII.) ; each organ has its own duct, which may or may not 

 join before entering the female antrum. This differentiation of 

 the " ovary " into two parts was first understood by 0. Schmidt. 

 Amongst the Rhabdocoelida we have instances of a pair of germaria 



