ZOOLOGICAL AWD BOTANICAL A8SOCIATI02C. 169 



through it, were soon collected, and the mass itself exhibited the 

 characteristics of cyst B. A constriction immediately took place, pro- 

 ceeding along the boundary of the mass of frustules at either extremity, 

 until the produced parts of the cyst presented the appearance of a 

 bag half closed at the mouth. These parts were obviously about to be 

 cut off, so as to form two Sporangia, one at either end of the cyst 

 (Fig. 11); but the process was obstructed by the evaporation of the 

 water. 



Previous to this I had noticed several cysts in which the granules 

 exhibited evident determination towards the opposite extremes, without 

 any sensible alteration in the general outline (Fig. 9) ; in others the 

 wall projected forwards at one side ; the produced part became full of 

 granules, and the opposite side, having lost its granular contents, 

 became perfectly pellucid, and exhibited so far the characters of variety 

 C (Fig. 10). 



These observations indicated with sufficient clearness the process of 

 the formation of Sporangia, and if anything were wanting, it was sup- 

 plied on the evening of the 3rd September, when I noticed a cyst with 

 a fully developed Sporangium connected with it. No doubt could be 

 entertained as to the Sporangium being attached to the cyst, for although 

 great force was applied to effect a separation, no pressure I could apply 

 was sufficient to disunite them (Fig. 12). 



The # result of the foregoing observations seems to be to confirm the 

 impression previously expressed, that the frustules of Diatoma vulgar e 

 enclosed in cysts exhibit a peculiar phase of actual conjugation, instead 

 of being an early stage in the development of the contents of a sporan- 

 gium produced by a conjugation of a preceding generation of frustules. 

 It is also apparent that in Diatoma vulgare the plant passes through the 

 several stages of its existence in the following order, — first, the young 

 frustules multiply by fission, and remain attached by their opposite angles 

 so as to form long filaments, until the season for conjugation arrives ; 

 then the filaments become compacted into a dense mass, and secrete a 

 hyaline cyst, into which the granular contents of the several frustules 

 are discharged ; next, the granules are collected, sometimes into one 

 sporangium, sometimes into two ; the sporangium next separates from 

 the cyst that produced it ; the cyst dissolves, and the withered frustules 

 yield up thoir vegetable life. 



