78 CO. Whìtman 



dipliygenic individuals are heterogeneons forms. They are alike in 

 origin, development. and adult form and structure ; bnt their germ-eells 

 pursue different courses of development, either because, contrary to ap- 

 pearances, they are fundamentally unlike, or as the result of conditions 

 that differ in some unknown respects ifecundation? food? position in a 

 cycle of generation» ? seasonal infiuences?) Cf. p. 61. 



7 . There is a remarkable correspondence between the age of the 

 host and tlie reproductive phenomena of the parasite. Nematogenic 

 individuals are abundantly represented in young Cephalopods i p. 33, 59) , 

 sometimes exclusively; while in adult Cephalopods Rhombogenic in- 

 dividuals are generally very numerous, and, in rare cases, appear to 

 bethe sole occupauts of the renal argan (p. 45). This fact may be inter- 

 preted in favor of a cyclical oeeurrenee of Rhombogenic reproduction 

 (p. 34), but can hardly be said to be analogous to the isolated oeeur- 

 renee of male and female Orthouectidae. Cf. Julin, 21 , p. 44; also 

 Van Beneden, 2, p. 209. 



8. The fact that the same individuai (diphy genie) may produce 

 consecutively infusoriform and vermiform embryos, is substantiated by 

 a variety of conürmatory phenomena, most of which are connected, 

 historically, with the origin of free nuclei in the axial cell (p. 34 — 47). 



The proof that some individuals (monogenie) produce throughout 

 only vermiform embryos , lies in the fact that adult Nematogens are 

 fouud in which the axial cell contains but one nucleus. 



9. The Rhombogenic mode of reproduction alone gives rìse to a 

 pluriuucleated axial cell. There are two classes of free nuclei appearing 

 in the axial cell in addition to the large central nucleus of this cell it- 

 self. The first class are, conjecturally , of the nature of polar globules. 

 Each germ-cell, before developiug into an Infusorigen, eliminates one 

 such corpuscle [n\ . These bodies (»parauuclei« agree in all their feat- 

 ures with nuclei, and are therefore called »free nuclei». The largest 

 number of such nuclei observed in any one case is eight, corresponding 

 to the number of Infusorigens. In pure Rhombogens, i. e. Rhombogens 

 that have not entered upon transitional phases , the whole number of 

 free nuclei — counting the original central nucleus — always exceeds 

 by one the number of Infusorigens. 



The second class of free nuclei are the »residual nucleii [n] of 

 the germogens [c] set free, as tlie final event in the history of the 

 Infusorigens. As there may be from one to eight Infusorigens in the 

 same individuai, and as one free nucleus marks the beginning, another 

 the end, of each Infusorigen, it foUows that a diphy genie Dicyeniid may 



