150 LIFE AND DEATH. 



development of the specific form. The Psorosperms were only 

 formed after the Gregarines had become established as a group. The 

 amoeboid organisms which creep out of them are in no way to be 

 regarded as the primitive forms of the Gregarines, even if the 

 latter may have resembled them, but they are coenogenetic forms 

 produced by the necessity for a production of numerous and very 

 minute germs. The necessity for a process of genuine develop- 

 ment perhaps depends upon the small amount of material contained 

 in one of these germs, and on other conditions, such as change of 

 host, change of medium, etc. It therefore results that the funda- 

 mental law of biogenesis does not apply to the Monoplastides ; for 

 these forms are either entirely without a genuine ontogeny and 

 only possess the possibility of growth, or else they are only endowed 

 with a coenogenetic ontogeny l . 



Some authorities may be inclined to limit the above proposition, 

 and to maintain that we must admit the possibility that we are 

 likely to occasionally meet with an ontogeny of which the stages 

 largely correspond with the most important stages in the phyletic 

 development of the species, and that the ontogenetic repetition of 

 the phylogeny, although not the rule, may still occur as a rare 

 exception in the Protozoa. 



A careful consideration of the subject indicates, however, that 

 the occurrence of such an exception is very improbable. Such an 

 ontogeny would, for instance, occur if one of the lowest Mono- 

 plastides, such as a Moneron, were to develope into a higher form, 

 such as one of the Flagellata, with mouth, eye-spot, and cortical 

 layer, under such external conditions that it would be advantageous 

 for the existence of its species that it should no longer reproduce 

 itself by simple fission, but that the periodical formation of a cyst 

 (which was perhaps previously part of the life-history) should be 

 associated with the occurrence of numerous divisions within the cyst 

 itself, and with the formation of germs. We must suppose either 

 that these germs were so minute that the young animals could not 



1 Butschli, long ago, doubted the application of the fundamental law of bioge- 

 nesis to the Protozoa (cf. ' Ueber die Entstehung der Schwarmsprosslings der Podo- 

 phrya quadripartita,' Jen.Zeit. f. Med. u. Naturw. Bd. X. p. 19, Note). Gruber has 

 more recently expressed similar views, and in fact denies the presence of develop- 

 ment in the Protozoa, and only recognizes growth (' Dimorpha mutans, Z. f. W. Z.' Bd. 

 XXXVII. p. 445). This proposition must however be restricted, inasmuch as a de- 

 velopment certainly occurs, although one which is coenogenetic and not palingenetic. 



