244 PROCEEDINGS OP THE AMERICAN ACADEMY. 



cells which I describe agree best with Heidenhaiu's '' Microcenter " and 

 " Centralkorper." Voa Leubossek employs Boveri's term " Ceutro- 

 som" as a unit, designating by it a group of numerous very minute 

 corpuscles held together by a " Zwischeumasse." He denies to each 

 granule or corpuscle in the group the individual value which Heidenhaiu 

 gives to each of his " Centralkorper." Von Lenhossek says ('95" ,p. 360) : 

 "Ich vermag die Beobachtungen Heidenhaiu's fur mein Object vollauf 

 zu bestatigen und mochte auf diese Zwischensubstanz besonderes Gewicht 

 legeu. Denn in ihrer Gegeuwart erblicke ich dasjenige, wodurch das 

 ganze Gebilde, mag es in seinem Innern noch so viele Kornchen be- 

 herbergen, doch immer in seiner Eigenschaft als einheitlicher Korper 

 gewiihrleistet ist." And again (p. 361): " Somit konnte ich micli bei 

 voller Anerkennung der Tragweite der Untersuchungen Flemming's und 

 M. Heidenhain's der von diesen Forschern eingefiihrten Terminologie 

 nicht anschhessen, bei der nicht das van Beneden-Boveri'sche Centrosom, 

 sondern die darein eingebetteten Kornchen als Centralkorper benannt 

 werden." 



In none of the cells which I have studied do I find any such large 

 number of minute granules held together by a " Zwischenraasse " as von 

 Lenhossek describes. Often I have seen two, three, or four corpuscles 

 in the centre of the sphere, but again, and more often, only one. This 

 condition agrees better with the Microceuter and Centralkorper which 

 Heidenhaiu describes. 



The single central corpuscle, if only one is present, or the group of such 

 corpuscles, if three or four are present, I call the centrosome. For the 

 surrounding clear zone, the " Centralscheibe," described by von Len- 

 hossek, it is best perhaps to employ his term " sphere," although the 

 use of the term sphere for this structure is here open to the same 

 objection as that which von Lenhossek urges : viz. it leaves out of 

 account the coarsely granular zone, which he proposes to call the 

 " Perisphere " or " Plasmasphere." 



Dehler ('9o) soon confirmed von Lenhossek's discovery. He found 

 a similar condition in the sympathetic ganglion cells of the same animal, 

 the frog. 



Radiations from the region of the centrosome are neither described 

 nor figured in the accounts given by either von Lenhossek or Dehler. 

 The details of the " Centralkorpergruppe " figured by Dehler are much 

 more nearly in agreement with the centrosome which I have described in 

 this paper than is the centrosome of von Lenhossek. Dehler's " Cen- 

 tralk()rpergruppe " agrees in its details with Heidenhain's Microceuter 



