G. Smith 2öl 



A compari.soii of Figs. a' — g"' witli Figs. 1 — 4' shows that the niass of chroinatin 

 does not alter in corrcspomlencc to the difterent sizes of tlie cysts. In Figs a — f 

 wliicli reprcsent cysts l)inlt in tiie warinth, it appears that the amoiuit of chromatin 

 is absoiutely as well as iclatively loss tiiaii in the other cases. It also tends to be 

 more scattered. 



(N.B. Whorc the ciiriiniatin luuips extended over more than onc scction they 

 have bcen inchided in tiie figure.) 



Froni the evidence that can bc gleaned froni Plates IL III. IV. the foliowing 

 rnle inay be fornuiiated: — Actinosphueria eucysting ander differeiit teiniieratures 

 oxhibit a difterent mass rehition betwcen chroniatin and cytoplasni, in tiie cold 

 the chroniatin being in excess, in the warmth the cytoplasm being in excess. 



Covclusion. 



Attention has been called to certain facts in the encystment of Actinosphaerium 

 Eichorni. Of these the niost important is that a different mass relation of 

 chromatin and cytoplasm may be induced in the unicellnhir cy.sts by the application 

 of heat and cold. 



From the different sizes of the cysts formed under similar conditions of 

 temperature, and from the widely different niimber of niiclei contained by free 

 living Actinosphueria of similar sizes and living under similar conditions of 

 temperature, it must be judged that temperature is not the sole cause of this 

 relation bctween chromatin and cytoplasm : analogy and a few fticts given above 

 point to nutrition as constituting the other chief cause. Whether the rule that 

 warmth diminishes the amount of chroniatin in proportion to the cytoplasm and 

 that cold increases it will prove to be of at all wide application it is inipossible to 

 .say from the absence at present of parallel experiments : experiments on this 

 head are now being made by Professor Hertwig at Munich which seem to point to 

 similar but wider conclusions. It is permissible to suggest that a deeper research 

 into this and kindred problems may reveal facts which will throw a light upon the 

 physiological differentiation of sex. 



EXPLANATION OF PLATES IL III. ANB IV. 



Plate II. Figs. a— f. Seotions through conjugation cysts built in tlie warm (24°— 2(5° C). Note 

 that in 5 the nuclei are not yet fused. 



Plate III. Figs. a'—n'". Sections through the conjugation cysts built in the cold (7° — 12° C). 

 Plate IV. Figs. 1 — i'. Sections through conjugation cysts built at rpom temperature (15° — 19° C). 



In all cases the figures bearing the same letter or number are from cysts produced by the same 

 Actinosphaerium. 



All figures drawn aceurately to scale under Zeiss objective DD, eye-piece 4. 



.v/ = siliceou3 cyst wall. 

 cj/=: cytoplasm. 

 eftr = chromatin. 



32—2 



