226 BIOLOGICAL LECTURES. 



from chromatin cannot be discarded as altogether too fanci- 

 ful, for numerous observations have indicated that some similar 

 process takes place. Thus Balbiani ('95) describes in the ciliate 

 Spirochona the origin of a body which he considers to be the 

 centrosome from the fusion of numerous granules of chromatin. 

 Ishikawa and I had grounds for thinking that the centrosome 

 in Noctiluca comes from the nucleus, while in Metazoa numer- 

 ous accounts have been given of the origin of the centrosome 

 from nucleoli and other intranuclear structures. The account 

 of the origin of the centrosome in the buds of AcantJwcystis y 

 which are formed after direct division of the mother-nucleus, and 

 which therefore contain no portion of the original centrosome, is 

 very suggestive. Schaudinn 1 ('96) asserts that, until the fifth day 

 after the bud is formed, there is no trace of a centrosome, but 

 during the fifth day a centrosome appears within the nucleus 

 and then makes its way into the cytoplasm, or rather the 

 nucleus moves away from the centrosome and assumes an 

 excentric position. Schaudinn does not say from what the 

 new centrosome is formed. 



While there is plenty of room for scepticism on Hertwig's 

 observations on the origin of the minute body which he calls 

 the centriole, the later history of this body is strikingly similar 

 to many recorded observations upon the sphere and centrosome 

 in Metazoa. The enlargement of the sphere and the persist- 

 ence of the centriole, as recorded by Lillie, Mead, Van der 

 Stricht, Sobotta, etc., may be described in almost similar terms. 

 But all of these cases are different from Actinospharium in that 

 the substance of the sphere is reported as forming a central 

 spindle between the centrosomes, and this structure, according 

 to Hertwig, is absent in the heliozoon. What then is the sig- 

 nificance of the intranuclear spindle fibers in this and in so 

 many other Protozoa where pole plates are present ? An 

 answer is immediately suggested by the relation which these 

 fibers have to the chromatin granules. Hertwig and Brauer 

 maintain that the granules are strung upon them into chromo- 

 somes, while Schewiakoff describes a similar connection in 

 Euglypha, and Schaudinn in Actinophrys. Central spindle 



1 Loc. dt. 



