NATURAL HISTORY OF THE DIATOMACEyE. 455 



and were obviously young frustules of the Cocconcma. It would appear 

 that production of the young frustules is preceded by the separation and 

 throwing off of the siliceous valves of the sporangium, and the constric- 

 tion or enlargement of its primordial utricle, according to the number of 

 young frustules originating in its protoplasmic contents. In this gather- 

 ing, forms of every size, intermediate between the minutest frustule in 

 the cyst and the ordinary frustules engaged in the conjugating, were 

 easily to be detected ; and the conclusion was inevitable that the cysts 

 and their contents were sporangia of the species with which they were 

 associated, and indicated the several stages of the reproductive process." 

 Although this observation seems to confirm the supposition that the con- 

 tents of the sporangium must divide into a number of small frustules 

 similar to the parents from which the sporangium sprung, yet further 

 study is necessary before we can consider this fact established ; and such 

 study can only be carried out by those who are willing to keep alive for 

 hours, days, or even weeks, such forms as they may meet with, and 

 spend hours at a time at the microscope, watching any change that may 

 take place in them. 



Thus do we see the diatomaceous frustule becoming gradually smaller 

 and smaller, through the carrying on of the process of self-division, and 

 its return to the normal dimensions through conjugation, or the forma- 

 tion of gigantic sporangia, whose cell-contents shall return by subdivi- 

 sion, and the genesis of motile spores to the size of the parent frustules. 

 A perfect cycle of changes would seem to be thus kept up, such as is by 

 no means uncommon in the life-history of many simple plants grouped 

 under the head Protophyta. And we are at the same time reminded, 

 when witnessing these changes and transformations, of the equally won- 

 derful metamorphoses, well known to naturalists, to take place in the 

 jelly-fish and hydroids of our coast, or those of the insect world, and 

 which we see going on day by day around us. The egg becomes a grub, 

 the grub a caterpillar, which, in turn, changes into the quiescent chrys- 

 alis, in which commonly the winter is passed, only to burst forth, as soon 

 as the revivifying rays of the spring sun warm it into being, as the gor- 

 geously tinted and active butterfly, the parent of innumerable eggs, 

 which shall in turn produce another generation of grubs. 



