494 Mr. Joseph Jackson Lister [Feb. 15, 



The point remained, however, a matter of inference until Schaudinn 

 pubHshed an account of the processes that he had observed, turning 

 inference into certainty. 



(It was only last June that we had to deplore the death of this 

 most brilliant investigator.) 



[The lecturer then read a translation of a passage from Schaudinn 's 

 paper,* in which the conjugation of zoospores, which there is good 

 reason to believe arose from different megalospheric parents, was 

 described. The growth of the resulting zygote (microsphere) was 

 observed by Schaudinn, until the little microspheric individual had 

 attained the five-chambered stage.] 



We are then, at last, able to give with confidence an answer to 

 the question. What is the significance of the phenomenon of dimor- 

 phism in the Foraminifera ? The answer is, It results from the 

 occurrence of two modes of reproduction in the life-history, sexual 

 and asexual. The megalospheric form is the product of asexual 

 reproduction, the microspheric form arises from the conjugation of 

 two similar zoospores, produced by individuals of the megalospheric 

 form. The Foraminifera thus fall into line with many other groups 

 of Protozoa, in which a similar alternation of generations has been 

 found. 



Attention was then directed to another remarkable phenomenon 

 presented by the shells of the Foraminifera — the multiform condition. 



In considering PolystomeUa and the nummulites we have been 

 dealing with forms in which the arrangement of the successive 

 chambers is uniform throughout growth. 



What is the controlling mechanism by which this uniform result 

 is brought about ? We have no evidence which will even suggest an 

 answer. The nucleus we know is an essential factor in the construc- 

 tion of the chamber wall, it in some way dominates the constructive 

 properties of the protozoan body, but the nuclear and protoplasmic 

 characters of many groups of Foraminifera are to all appearance 

 alike, yet they build their shells on widely different plans. 



But, leaving the i)roblem of the nature of the controlling 

 mechanism as at present insoluble, to return to its effects we find that 

 in several groups of Foraminifera, the shells are not built on the same 

 plan throughout, but that two or even three laws of grow^th have 

 controlled the building of the shell at successive periods. 



[A lantern sHde displaying the form of the shell in Spiroplecta, 

 Biyenerina and CJavulina was here shown.] 



Thus, among the Textularidae, the genus Spiroplecta is charac- 

 terised by a planis|)iral arrangement during the earlier stage of 

 growth, but later in life the shell is formed of alternating chambers 



♦ Untersuchungen iib. d. Fortpflanzung einiger Rhizopoden. Arb. aus 

 Kais. Gesundheitsamte. Bd. xix., Heft 3, 1903. 



