PRESIDENTIAL ADDRESS. 593 



chromidia ttnd cliromidial net of Hertwig were comparable with the strands of 

 staining substance which had been described in the Foraminifera. In tracing out 

 the very interesting life-history of Centropyxis he showed that, as in the Forami- 

 nifera, the nuclei of the gametes are derived from the chromidial net, while here 

 also the vegetative nucleus disappears. Comparable structures were also shown 

 to exist in Chlamydophrys, a species of Amosha, and in Entamceba.'^ Schaudinn 

 found that in all the cases investigated by him the nuclei of the gametes are derived 

 from the chromidia, whether diffused or united into a reticulum, and concluded 

 that the chromidia are in fact the substance of the nuclei of the sexual cells. He 

 also instituted a very enlightening comparison with the Infusoria, the macro- 

 nucleus of which, formed at the division of the zygote nucleus and disintegrating 

 prior to conjugation, he compared with the vegetative nucleus of the Rhizopoda, 

 while the micronucleus finds its homologue in the more or less dispersed chro- 

 midia. 



By this comparison a number of previously isolated phenomena fall into line. 

 The nuclearapparatus of the Infusoria, differentiated into vegetative and repro- 

 ductive portions, finds, though not an explanation, at least a parallel in other 

 groups of Protozoa. The scattered chromidia of the Foraminifera are thus con- 

 nected with the chromidial nets of monothalamous Rhizopods, which present 

 various degrees of compactness, and through them with the definitely rounded 

 Infusorian micronuclei. In the involved streaming movements which precede the 

 separation of the protoplasm of the mierospheric parent into the megalospheric 

 brood we may recognise a process of equal distribution of the minutely divided 

 chromidia through all parts of the mass which is about to divide, leading to their 

 transmission in equal portions among the ofi'spring. 



The fact that in the Foraminifera, at any rate, the chromidia are directly 

 derived from the vegetative nuclei, though they increase in size independently, 

 is at least some acknowledgment of the hereditary principle in the transmission 

 of nuclear material, though we have at present no evidence whatever to show that 

 the foci about which they gather to form the nuclei of the megalospheres or the 

 mother nuclei of the zoospores are in any way derived from pre-existing nuclei. 



Though light appears ahead, it seems to me that we are not yet at liberty to 

 consider ourselves out of the wood. The comparison of chromidia with infusorian 

 micronuclei has brought us a long way from Hertwig's original observations in 

 Actinosphariu7n of the dependence of the formation of the chromidia on states of 

 metabolism ; moreover, no evidence has as yet been found that in Actinosphcerium 

 the gametic nuclei are formed from chromidia. 



In comparing the abundant deeply-staining chromidia of the Foraminifera with 

 the Infusorian micronucleus, so poor in chromatin, Schaudinn ascribes the 

 difference to the fact that in the former, as in Rhizopods in general, the formation 

 of the brood (of zoospores) occurs by simultaneous multiple fission, and is connected 

 with the act of fertilisation, so that sufficient chromatin to provide for the nuclear 

 equipment of each of the thousands of zoospores must be ready in the parent as it 

 approaches the reproductive stage. In the Infusoria, on the other hand, where the 

 gametes are the ultimate product of a succession of binary fissions there is never 

 the occasion, at any one time, for so large a store of chromatin in the body.* 

 While admitting that there is much force in this explanation, we may notice 

 that in Polystomella the formation of the chromidia begins early in the 

 growth of the mierospheric individuals, and they are in my experience very 



' Calkins in his very interesting observations on Ama-la proteus also found that 

 the chromidium-like bodies are derived from the vegetative nuclei. See his paper 

 ' Evidences of a Sexual-cycle in the Life-history of Amtvba protevs ' Arch f Protis 

 tenkunde, Bd. v. H. 1 (1904). 



2 I have here considerably expanded what I take to be Schandinn's meaning His 

 words are {I.e., p. 553) : ' Die Chromidien (of Polystomella) entsprechen den in der 

 Em- Oder Mehrzahl vorhandenen Geschlechtskernen oder Mikronuclei der Infusorien 

 Der Unterschied besteht nur darin, dass wegen der Verknupfung der Brutbildune 

 DQit den Kopulationsvorgangen die Geschlechtskernsubstanz bei Polystomella in 

 viel grosseren Quantitaten vorhanden ist, als bei den Infusorien ' 



1906. ■ QQ 



