36 C. 0. Whitman 



and is easily recognized from other miclear bodies by its greater volume 

 and more elougated form. But it frequeutly happens that all these 

 meaus of recognition are lost: its position may be in the head or the 

 tail, or in any part of the body; it may exhibit a spherical form and 

 differ so little in size from neighboring nuclei that discrimination be- 

 comes impossible. 



Both Khombogens and Nematogens arise from vermiform embryos 

 like that seen in tìg. 1 ; and it is impossible at this stage to predict 

 which forni will be brought out by subsequent development. 



Shortly before , or soon after the embryo escapes from the parent, 

 we find four germ-cells — two before and two behind the nucleus (fig. 95, 

 PI. 5) . Next Comes a stage of eight germ-cells arranged in a single 

 loose row along the middle of the axial cell — four before and four 

 behind the centrai nucleus (fig. 100, ne\. It is about this time that the 

 first indications are gi\ en of the kind of reproductive activity the indi- 

 viduai is destined to display. The continuation of the same mode of 

 multiplication leads to the Nematogenic condition , represented by more 

 or less numerous germ-cells scattered along the axial cell and by a 

 single large nucleus geuerally occupying a centrai position. Ali adult 

 Nematogens which show ouly one large nucleus in the axial cell are 

 Nematogens by direct development . and , so far as I bave been able to 

 ascertain, never produce but one kind of embryo, namely, the vermi- 

 form. It may be convenient to designate such individuals primary 

 Nematogens. 



The Rhombogenic condition is introduced after a certain number of 

 cells — seldom more than from four to eight — bave arisen from the 

 two primary germ-cells. Instead of pursuing further the primary, or 

 Nematogenic mode of multiplication by simple division , each of these 

 cells (»germogens« of Van Beneden) becomes a center of proliferation, 

 producing cells which are compactly and more or less concentrically 

 grouped around the mother celi, as described by Van Beneden. An 

 interesting event takes place preparatory to the introduction of the 

 Rhombogenic mode of cell-multiplication. This event, which completely 

 escaped the attention of Van Beneden, consists in the elimination from 

 the celi of a body analogous to a polar globale. Whether this body is 

 the physiological equivalent of the polar globale so widly known among 

 Metazoa, is a questi* m I am unable to answer. The reasons to be urged 

 against such an Interpretation are important, though not quite conclu- 

 sive to my mind. Nothiug that could be called fecundation has yet 

 been discovered ; but the chief objection lies in the fact that the celi 



