40 C. 0. Whitman 



Phenomena of Transition. 



The closing events in the history of the Infusorigen form at once 

 the end of one aet and the begiuning of another in the drama of re- 

 production. This transitional state is seen in figures 112 and 113, 

 both taken from the same Dicyememiea Eledones (2.40 mm long). 

 These two figures show all that the axial cell contained , except the 

 central nucleus. We see here two paranuclei (w'), and the final prod- 

 ucts of two Infusorigens, namely , two defunct germogens (c) , each in- 

 closing a residual nucleus [n] , and two Clusters of germ-cells [vg] . The 

 germogen has finished its work ; its reproductive energy has departed. 

 What becomes of its protoplasmic body I am unable to say ;^but it prob- 

 ably dissolves, leaving the residual nucleus free. The germ-cells are, 

 in one case, loosely aggregated around the germogen , but they can no 

 longer be said to form the envelope of an äctive Infusorigen. These 

 germ-cells agree fully with the germ-cells found in Nematogens , both 

 in size, in general aspect, and in their incoherent order. A comparison 

 of these figures with 1 1 and 1 1 1 shows how widely dififerent in these 

 respects are the germ-cells destined to produce infusoriform embryos. 

 The last germs produced by the germogen differ from those of preceding 

 generations in being much smaller, in having relatively smaller nuclei, 

 and in showing no teudency to form anything like an organic group. 

 They diflfer still further in possessing the power of multiplication by di- 

 vision, as shown in figures 114 , 115 , where the loose arrangement of 

 the cells correspouds exactly with what is seen in figs. 1 and 14, PI. 1. 

 In the Rhombogen, on the contrary, there is no multiplication by divis- 

 ion outside the Infusorigen. The germ-cells [ig] in fig. 1 1 1 are under- 

 going developmental, not multiplicative division It is a pro- 

 cess of cleavage rather than simple fission. 



Fig. 117 contains two examples of a transitional kind. The D. 

 moschatum from which this was taken contained , besides the central 

 nucleus, four such assemblages as are seen in the figure, in all of which, 

 except one, a residual nucleus was present. It is possible, if not prob- 

 able, that this nucleus was present, although not visible, in the Cluster c. 

 The cells vg , seen in these figures, continue to multiply until, in many 

 cases, the entire axial cell is loaded with them. Sooner or later they 

 begin to develop into vermiform embryos. 



The last generation of cells produced by the Infusorigen is not 

 then homodynamous with those of prior origin. The appearance of this 

 generation marks the introduction of a new order of propagation, — 



