SPIROGYRA 225 



the collection of the two halves at the poles of the spindle as 

 the new nuclei, which are still connected by fine threads. 



4. The subsequent dilatation of the spindle, the threads 

 becoming more curved, while from it new connecting threads 

 pass to the peripheral protoplasm. 



5. Meanwhile microsomata collect at the equator of the 

 dividing cell. 



6. Note also the involution of the chromatophores and their 

 subsequent division. 



7. The gradual formation of the septum, beginning at the 

 periphery and proceeding towards the centre. 



III. In summer or autumn the process of conjugation and 

 formation of the zygospores may frequently be observed in 

 Spirogyra: filaments which are about to conjugate assume a 

 position parallel to one another, and on them the following 

 observations are to be made 



1. Cells opposite one another put out rounded processes, 

 which meet. 



2. The wall at the point of junction is absorbed, and thus the 

 canal of communication is formed. 



3. Meanwhile the protoplasm of the two cells has rounded 

 off, one (the male) usually doing so earlier than the other (the 

 female). 



4. The protoplasm of the male cell passes through the canal, 

 and coalesces with the female to form the zygote. 



5. The zygote surrounds itself with a thick stratified cell-wall, 

 which is smooth or shows various markings of the surface 

 according to species. 



