144 SCIEXCE PROGRESS. 



he calls the archoplasm. Of all the so-called organs of the 

 cell, none has been more vigorously investigated with so 

 little agreement in general result as the centrosome, or 

 centrosphere. In fact, when one dips into the bulky litera- 

 ture which has grown up around this body, the dimensions 

 of which sometimes border on, and often dip below, the 

 visible, one is filled with admiration at the vastness of the 

 labour, and with sorrow at the utterly incommensurate 

 result. Perhaps the great interest attaching to it is to be 

 largely attributed to the clearness with which it presented 

 itself to \^an Beneden in Ascaris,^ in which animal its im- 

 portance was first insisted on. In many other animal cells 

 it is also clearly seen, and I may say that in another in- 

 vertebrate animal I have, thanks to the kindness of Professor 

 Rlickert in Munich, seen centrosomes almost surpassing 

 those of Ascaris itself But, on the other hand, there are 

 many other animals in which these structures appear under 

 a simpler form. The dense aggregation of protoplasm is. 

 not observed in a number of cases even at the time most 

 favourable for distinguishing it if present. Again, even in 

 Ascaris, it would seem that it is not exactly a permanent 

 niorpJiological constituent of the cell ; for Boveri and others 

 had observed that it becomes indistinguishable at a later 

 stage of nuclear division. Here, then, we must assume a 

 " physiological " persistence, or use some other expression 

 to save the individuality of the "cell organ". But is it 

 really necessary to regard the centrosome as a universally 

 essential structure at all ? We know that, curiously enough,, 

 in the divisions which result in the cutting off of the 

 polar bodies from the maturing ovum, it is very com- 

 monly and perhaps typically absent, and there is a large 

 amount of positive evidence to show that with the single 

 exception of Myzostoma, described by Wheeler,'- and ap- 

 parently well authenticated, it is entirely lacking from the 



^ E. van Beneden et Neyt, " Nouvelles recherches sur la fecondation et 

 la division mitotique chez I'ascaride megalocephale," Bull. Ac. Roy. de- 

 Belgigue, 1887. 



- " The behaviour of the centrosomes in the fertilised egg of Myzostoma 

 glabra," Leuckart, y<?///-. of Morph., vol. x. 



