PHENOMENA ACCOMPANYING FERTILIZATION 513 



demand for further experimental evidence. Indeed some embar- 

 rassing questions based upon what we already know must be 

 answered: If it is environment alone what are the external condi- 

 tions res])onsible for the formation of the gametes in Coccidiomorpha, 

 Gregarinida, Foraminifera and Phytomonadida? Or in the ciliates 

 what is the explanation of the failure of external conditions to 

 induce conjugations in some lines and not in others? Or why will 

 the same external conditions fail with youthful forms when they are 

 successful with older (mature) forms? 



In practically any epithelium deeply infected with coccidia 

 adjacent cells contain vegetative stages of the organism, agamont 

 stages in reproduction, gametocyte stages of both kinds, and nearby 

 are zygote stages. If conditions of the infected host cell are respons- 

 ible for the different phases it must be a very delicate difference 

 that calls out asexual reproduction in one and gamete formation 

 in another, and all within the radius of a single field of the micro- 

 scope. If products of degeneration of an infected host cell cause 

 gametocyte differentiation in one organism why do not the products 

 of the cell next to it produce a similar effect on its contained organism 

 instead of which we find the latter reproducing asexually? The 

 conception of external factors as the sole cause of protoplasmic 

 changes leading to fertilization must be very elastic to cover such 

 cases. Why are not all malaria parasites transformed into gameto- 

 cytes if the blood is the determining factor? Plasmodium livax 

 taken into the gut of the mosquito should be transformed into 

 gametocytes producing gametes instead of which only gametocytes 

 already formed produce gametes while agaraonts are apparently 

 digested; and in the blood of man or birds these gametocytes 

 circulate with the vegetative forms and with agamonts. Surely 

 in these parasitic forms, granted that external conditions may be 

 provocative some internal condition of the organism nevertheless 

 predetermines the action of the environmental stimuli. 



With ciliates every experimentalist knows that in pure line work 

 conjugation tests are sometimes successful, sometimes not. Jennings 

 (1913) noted this in different races of Paramecium; Woodruff for 

 se\'eral years was unable to obtain a single pair from his famous 

 culture of Paramecium aurelia, although ultimately they did 

 conjugate; Calkins and Gregory (1914) cultivating the first eight 

 individuals from an ex-conjugant of P. caiidatum in pure lines, 

 found that conjugations were abimdant in certain lines whenever 

 a test was made, while other lines remained negative at every test 

 until the race was many months old. Similar tests made with any 

 series of Uroleptus mohilis, and by test we mean a period of rich 

 feeding followed by hunger, is negative if the organisms are young, 

 positive if the organisms are mature (F'ig. 204, p. 491). All of 

 these facts, and the literature contains many other similar cases, 

 33 



