553 In the case of Globigerina, some fourteen species (out of a very much larger number of described forms) were allowed by Brady (in 1884) to be distinct; and this list has been, I believe, rather added to than diminished. But these so-called species depend for the most part on slight differences of degree, differences in the angle of the spiral, in the ratio of magnitude of the segments, or in their area of contact one with another. Moreover with the exception of one or two ãdwarfã forms, said to be limited to Arctic and Antarctic waters, there is no principle of geographical distribution to be discerned amongst them. A species found fossil in New Britain turns up in the North Atlantic: a species described from the West Indies is rediscovered at the ice-barrier of the Antarctic.
554 Dreyer, F., Principien der Gerû¥stbildung bei Rhizopoden, etc., Jen. Zeitschr. XXVI, pp. 204ã468, 1892.
555 A difficulty arises in the case of forms (like Peneroplis) where the young shell appears to be more complex than the old, the first formed portion being closely coiled while the later additions become straight and simple: ãdie biformen Arten verhalten sich, kurz gesagt. gerade umgekehrt als man nach dem biogenetischen Grundgesetz erwarten sollte,ã Rhumbler, op. cit., p. 33 etc.
556 ãDas Festigkeitsprinzip als Movens der Weiterentwicklung ist zu interessant und fû¥r die Aufstellung meines Systems zu wichtig um die Frage unerûÑrtert zu lassen, warum diese Bevorzû¥gung der Festigkeit stattgefunden hat. Meiner Ansicht nach lautet die Antwort auf diese Frage einfach, weil die Foraminiferen meistens unter VerhûÊltnissen leben, die ihre Schalen in hohem Grade der Gefahr des Zerbrechens aussetzen; es muss also eine fortwahrende Auslese des Festeren stattfinden,ã Rhumbler, op. cit., p. 22.