The Microscope. 19 



still persisting. In a short time the process is carried further, 

 and the result is as shown in Fig. 1. At last the nucleus dis- 

 appears. 



The next step is the formation of what is known as an am- 

 pinaster, a peculiar arrangement which always precedes cell- 

 division. The granules of protoplasm and deutoplasm become 

 arranged in the shape of a spindle, and in sections look almost 

 exactly like the peculiar figures seen when iron filings are ex- 

 posed to the influence of a powerful mngnet. Between the two 

 poles they form lines like the meridians on a map, while in 

 other directions they radiate from the poles, giving the extrem- 

 ities a star-like appearance. One end of this amphiaster is near 

 the surface of the egg, the other is at some distance below it. 

 Soon from the outer end of the spindle a slight protrusion is 

 seen, an'd a portion of the egg is extruded ; this is the first polar 



Pig. 2.— Formation of polar globules; a, amphiaster; /, female pronucleus; 

 p', first polar globule; \/ / , second polar globule. 



globule. Soon the process is repeated and a second polar glob- 

 ule is formed, and occasionally still more. The remainder of 

 the amphiaster now sinks to near the centre of the egg, and 

 forms what is known as the female pronucleus. 



Before considering the meaning of this phenomenon, let us 

 turn for a moment to the formation of the male reproductive 

 elements, known as the spermatozoa. In the male reproductive 

 organs are certain cells, originally not distinguishable from 

 those which produced the eggs. These cells give rise to the 

 spermatozoa, several or many of which are formed from a single 

 cell. When ripe the cell breaks down and the speimniozoa 

 escape, but it is especially to be noticed that so far as we know 

 the whole of the cell does not become converted into repro- 

 ductive elements, but that a certain portion remains behind. 



Now, what is the explanation of these facts ? It is not cer- 

 tainly known, but the following hypothesis, put forth almost 

 simultaneously by Balfour and Minot, has considerable plausi- 



