Evidence from Vroior.oans 375 



besides cliromatin enters into tlieir ))r()(liK'ti()ii. The lollowinp 

 paragrapli from Tonniges tells the story in outline. '"I'richoeysts 

 in the act of origination whieh I have designated as trieiioeliro- 

 midia, present two substanees. One is intensely eolored with 

 the nnelear staining mediiun employed {ach, figure 'J 1 ) . so must 

 be regarded as ehromatin. The other remains mieoiored aud eon- 

 sequently is held to be aehromatie substance {achr, figure tjl). 

 The first produces the axial rod of the future triehocyst. while 

 the latter, the achromatic substance, produces the external en- 

 velope and the myoneme-like structure." ' Four stages in the de- 

 velopment of a triehocyst are shown in figure 21 a, b, c, d. Natur- 

 ally many detailed structural changes not here noticed in both 

 the axial part and the enveloping part occur before the organ is 

 completed and ready for use. But these need not concern us 

 since they in no way affect the main point, namely that evi- 

 dence that the achromatic substance of the macronueleus is 

 the physical basis of heredity of organs under consideration, 

 comes from exactly the same source and is exactly as valid as 

 is the evidence that chromatin jdays such a role. 



The question of whether the cytoplasm of the animal plays 

 a direct part in the development of these organs, while very 

 important were we seeking for an adequate general theory 

 of development or for complete knowledge of the factors 

 involved in this particular development, must not detain 

 us since all we are concerned with in this section is to find 

 whether any substances other than chromatin are diter- 

 niincrs of hereditary attributes. 



(e) The Skeleton of liadioJarla 



With these Illustrations from the infusoria of sub- 

 stances other than chromatin which serve as the physical 

 basis of heredity, we must turn from the endless cxami)les 

 that might be drawn from the same grouj), aiul pass to 

 another great sub-division of the proto/oa, the Kadlolaria, 

 for a few illustrations. In the chaj)ter on the general 

 ontogeny of the protozoa we spoke particularly of H.-icker's 

 studies on the development of the skeleton in tli. Aiilo- 



