VAN NIEL SYSTEMATICS OF THE BACTERIA AND BLUEGREEN ALGAE 91 



phylogenetic standpoint it is hardly surprising that a major problem would 

 exist; it is, in fact, inherent in the concept of evolution itself. 



Acceptance of the doctrine of organic evolution implies that the clearly 

 recognizable forms of plant and animal life must have had a beginning in some 

 far more primitive ancestry. It does not appear unreasonable to envisage the 

 evolution of an elementary "molecrobe" to typical plants and animals, respec- 

 tively, as having passed through intermediate stages of increased complexity 

 which, in a number of respects, would have the characteristics of "bacteria." 

 Such intermediate stages are themselves neither plants nor animals; they occupy 

 a position in the realm of living organisms that is antecedent to the emergence 

 of the later developmental stages, and display characteristics of both major 

 kingdoms. It is not the contention of this argument that the present-day bacteria 

 are, in effect, such intermediate stages; it is easily conceivable that they might 

 represent organisms that have evolved from the same precursors from which also 

 the typical plants and animals, by different routes, originated. 



As early as 1866 this situation was clearly recognized by Haeckel, who wrote 

 (1:202-203) : 



Wir finden in den bekannten Thatsachen durchaus keine Nothigung fiir die An- 

 nahme, dass alle Organismen-Stamme entweder Thiere oder Pflanzen sein miissen. Viel- 

 mehr miissen wir die bisher giiltige exclusive Zweitheilung in Thier- und Pflanzenreich 

 in dieser Beziehung fiir niclit begriindet eracliten. Es ist schon von verschiedenen 

 Seiten darauf aufmerksam gemacht worden, dass es sowohl fiir die Zoologie als fiir die 

 Botanik ein grosser Gewinn sein wiirde, wenn man die vielen zweifelhaften Lebewesen, 

 die weder echte Thiere noch eclite Pflanzen sind, in einem besonderen Mittelreiche oder 

 Urwesenreiche vereinigen wiirde; doch hat unseres Wissens noch Niemand den Versuch 

 gemacht, ein solches neues Reich der Urwesen nach Inhalt und Umfang fest zu bestim- 

 men, und seine Begrenzung wissenschaftlich zu begriinden und zu rechtfertigen. Wir 

 wagen hier diesen Versuch auf Grund der obigen Deductionen und schlagen vor, alle 

 diejenigen selbststandigen Organismen-Stamme, welche weder dem Thier- noch dem 

 Pflanzenreiche mit voller Sicherheit und ohne Widerspruch zugeeignet werden konnen, 

 unter dem Collectivnamen der Protisten, Erstlinge oder Urwesen, zusammenzufassen. 



In this new kingdom the bacteria, along with such dubious organisms as 

 Protogenes and Protamoeba, were allocated to the first phylum, Moneres, com- 

 prising, in Haeckel's words, "the completely structureless and homogeneous or- 

 ganisms which consist solely of a bit of plasma (a mucoid protein compound), 

 obtain their nutrients simply by endosmosis, and reproduce by schizogony or 

 .sporogony" (1866, 2:20). 



Unquestionably there is much that can be said in favor of Haeckel's third 

 kingdom. Nevertheless, its acceptance raises a new problem to which P. W. 

 Andrewes (1930), following Kent (1880-1882) and Biitschli (1880-1889), has 

 called attention^n the statement (p. 298) : 



To revive Haeckel's third kingdom of "Protista" for organisms so low down in the 

 scale that they cannot definitely be assigned to either of the other kingdoms, may be a 

 useful expedient, but it is a doubtful gain, for it necessitates two arbitrary lines of 

 demarcation in place of one. 



The seriousness of this problem becomes at once apparent when one considers 

 the extreme paucity of characteristics which one is compelled to associate with 

 the early forms of life, the pre-plant and pre-animal organisms for which the 

 kingdom Protista was proposed. Morphological and developmental features must 



