HISTORY OF DIATOMS. 



*5 



i. Two valves, a connecting part and a necleus " 



( fi g- ") 



, , r early stage. 



2. Two valves, two connecting parts and a necleus 



(fig- J 



3. Two valves, two connecting parts, and two nuclei ] 



(fig. 8) 1 More or less 



4. Four valves, two connecting parts, and two nuclei 



(fig. 10) 



5. Four valves, four connecting parts and two nuclei 



(fig- 9) J 



"The external connecting part of frustules is often caducous and detaches 

 itself spontaneously ; this is a fact which must be taken into account. 



advanced stage 

 of deduplica- 

 tion. 



Fig. 10. 

 Fig. 10. Diatom [Isthmia) formed of four valves and two connecting 

 Fig. 11. The same with two valves and one connecting part. 



" It is well also to notice that the protoplasm of the primordial utricle 

 generally travels into the interior of the silicious envelope both previously to 

 the commencement of the sub-division of the utricle and again after the 

 termination of the phenomenon, drawing along with it the endochrome ; and 

 also that the migrations of the colouring matter vary in their nature according 

 to the genera and families of diatoms. While a diatom divides by binary 

 sub-division, the endochrome also separates into two parts in order to 

 apportion half of it to each of the two new utricles. 



" Every diatom frustule, it will be noticed, consists of an old valve (fig. 

 1 F', fig. 8 F) from the original frustule and a younger valve (fig. 1 F and 

 fig. 8 F') of subsequent creation, whose connecting part, when it is developed, 

 slides in the inside of the connecting part of the old valve. It follows from 

 this that in the large majority of diatom genera where the connecting parts 

 are of the exact breadth of the valves and are even of smaller diameter to 

 them, every sub-division must effect a diminution in the dimensions of the 

 new frustule equivalent to double the thickness of the connecting part. The 

 thickness of the latter being known, it can, even a priori, be determined what 

 will be the size of any descendant after any given number of sub-divisions." 



The above opinion expressed by Mr. Deby is that held by Diatomphiles 

 for a long time, but it does not completely account for all the facts. If the 



