BLACK.MAN : THE SPERMATOGENESIS OF SCOLOPEXDRA. 99 



ulatity which it often exhibits in its reaction to various stains. "When 

 we compare the simple granule representing this structure in the male 

 cells of insects, with the comparatively immense, complicated structure in 

 the eggs of Liruulus described under the same name by Munson ('98), it 

 must be seen at once that either the centrosome exhibits a great dissimi- 

 larity in different cells, or very different structures have been included 

 under one term. As a matter of fact there is much discussion as to what 

 structure shall be designated by the term centrosome. Wilson ("95 1 ') 

 expresses this as follows : "The word 'centrosome ' is at present used in 

 three different senses, being applied (1) by Boveri to the entire central 

 mass of the aster exclusive of the rays (" astrosphere " of Fol, "centro- 

 sphere" of Strassburger), (2) by Strassburger and others to a smaller 

 dark body often found within the centrosphere, and (3) by Heidenhain 

 to the individual granules of which this dark body is made up." Since 

 this was written, many new facts in connection with the centrosome have 

 been discovered, but the confusion in the terminology has not been 

 rendered less marked by these observations. Indeed, owing to the 

 greater number of individuals engaged in these studies, the confusion of 

 terms seems to have increased rather than lessened. This fact is greatly 

 to be deplored, for in making a comparison of apparently identical struc- 

 tures described under various names by different authors one is often at 

 a loss in attempting to correlate the results. 



Boveri (:01), in his work upon the nature of the centrosome, gives at 

 various places the characteristics by which one may distinguish the cen- 

 trosome and the ceutriole. The centrosome is in his view that part of 

 the structure found at the centre of the aster during mitosis which is 

 present at all stages of cell division and divides to form the centres of 

 the daughter cells. He gives as a rule : " Ein Korper, an den die 

 Spharenradieu direkt herantreten, ist das Centrosoma." Division of the 

 centrosome is always preceded by the division of the ceutriole. "Das 

 Centriol teilt sich betrachtlich friiher als das Centrosom." This division 

 generally occurs at the time of the formation of the equatorial plate, but 

 may take place earlier (Echinus) : " Die Teilung des Centrosoms selbst 

 scheint dagegen nomaler Weise nigends friiher als in der Metakinese zu 

 beginnen . . . Doppelkorner zur Zeit der Aequatorialplatte oder friiher, 

 werden also mit grosser Sicherheit als Centriolen in Anspruch genomineu 

 werden diirfen." The centrosomes arc, "Die grossere der beiden in 

 einander gesohalteten korperlichen Differenziernngen im Centrum der 

 Spharen." The centrioles are the smaller central bodies and are " von 

 so extremer Kleinheit, dass sie selbst in den grossten Zellen, wie den 



