A Contribut. to the Embiyol., Life-history, and Classificat. of the Dicyeoiids. 39 



plain this point. Thus far we bave seen only two kinds of free nuclei in 

 the axial cell — paranuclei and the centrai nucleus. Another set of 

 nuclei , quite dìstinct in origin and time of appearance , is now to be 

 accounted for. Van Beneden has correctly stated the origin of this third 

 class of nuclei , but he failed to recognize that their appearance marks 

 the vanishing point of the Khombogenic phase of life. »A germogen, « 

 says Van Beneden, »can produce only a limited number of generations 

 of germs. The celi gradually exhausts itself. The protoplasmic body of 

 the celi is entirely used up in the formation of the last generation ; the 

 nucleus is then ali that remains of the germogen. It is found at first in 

 the middle of the rosette formed by the last germs grouped around it ; 

 but the rosette ends in disaggregation : the germs separate from one 

 another , and the nucleus of the germogen is then found in Suspension 

 in the protoplasmic reticulum of the endodermic celi , which becomes 

 polynucleated.« (1, p. 53 — 54.) 



Thus there arise in the course of the history of every Infusorigen 

 two nuclei; one, the paranucleus, appears as a preparatory step to 

 the development of the Infusorigen ; the other, which may be called the 

 residuai nucleus, is what remains after the role of the Infusorigen is 

 played. As the several Infusorigens found in a single individuai may 

 not reach the concluding point of their productivity simultaneously , it 

 follows that the number of free nuclei in a Rhombogen may exceed the 

 number of Infusorigens by more than one ; and this explaius the case, 

 abovenoted, of seven Infusorigens and nine free nuclei. One of the 

 seven Infusorigens had ended its career, and perhaps we might say its 

 existence. The paranucleus , the residuai nucleus , and a loose group 

 of cells were ali there was left of it. Stili it may be said that the num- 

 ber of free nuclei for the pure Rhombogenic state is one more than the 

 number of Infusorigens , since the appearance of residuai nuclei simply 

 marks an epoch of transition from the Rhombogenic to the Nematogeuic 

 mode of reproduction. Allowing that such a transition takes place, and 

 that the free nuclei arise in the manner described , we bave an expla- 

 nation of the plurality of nuclei in the axial cells of many Nematogens, 

 and further, of the fact that the number of these nuclei is odd. A single 

 nucleus in a Nematogen indicates that the individuai is a Nematogen 

 by direct development ; three nuclei show that the individuai has passed 

 through a Rhombogenic stage in which only one Infusorigen was pres- 

 ent; five, seven, or nine nuclei point in the same way to the prior 

 existence of two , three or four Infusorigens. 



