HISTORY OF THE EGG FROM FERTILIZATION TO CLEAVAGE. 31 



to " thread metamorphoses," and it is now known that the chromatic ele- 

 ments do not always undergo such metamorphoses. 



Aster is limited to the achromatic radial figures, and is not to be con- 

 founded with the chromatic aster of Flemming. Amphiaster (Fol) appears 

 to serve well as a name for the whole figure presented in the spindle 

 and its astral poles. The caryokinetic figures appearing in the formation 

 of the polar globules may be called polar amphiasters, or polar spindles, in 

 preference to direction spindles or archiamphiasters (Whitman). 



The terms chromatic and achromatic, introduced by Flemming, are still 

 in general use, in spite of the fact that they do not quite meet the needs 

 of the latest analyses. For finer distinctions, we have followed the sug- 

 gestions of Boveri and Bohm, but we are not fully contented with such 

 names as spermato- and ovo-merites. Platner has used canjosomes for the same 

 elements ; and, following in this line, we might suggest arsenosomes and 

 thelysomes for sexual distinction. 



Btihni calls attention to what appears to be a very important distinction. 

 He finds that the merite, or caryosome, is composed of two parts, a pe- 

 ripheral substance that stains feebly, and a minute central corpuscle that 

 stains deeply. The latter he calls a microsome. The peripheral portions 

 of the cai vosomes melt together, and the microsomes thus set free are 

 identified with the elements (chromatic loops, granules, etc.) of the equa- 

 torial or axial plate of the spindle. 



We do not find in the development of the fish egg any indication of the 

 so-called akinetic or amitotic division of the nucleus ; and allowing that such 

 a mode of division exists, we should prefer direct division to either of these 

 terms. Flemraing's objections to akinetic, and Carnoy's objections to ami- 

 totic, are sufficient in our minds for the rejection of both terms. 



It may not be out of place in this connection to express a doubt as to 

 the need of a term for what has been called direct division. The evidence 

 of such division is mainly of a negative character, and it is safe to say 

 that not a single case has been placed beyond the reach of reasonable 

 doubt. Numerous alleged cases have turned out to be strictly caryoki- 

 netic, and the drift of discovery is unmistakably towards the establishment 

 of uniform laws in nuclear division. 



The idea advanced by some authors, that caryokinetic division has 

 arisen through developmental stages from some relatively simple process, 

 such as direct division is conceived to be, is not even plausible. Had 



