286 



CONJUGATION OF DIATOMACE^. 



exactly as among the Desmidiacese. Thus in Surirella (Fig. 129) 

 the valves of two free and adjacent frustules separate from 

 each other at the sutures, and the two endochromes (probably in- 

 cluded in their primordial utricle) are discharged ; these coalesce 

 to form a single Sporangia! mass, which becomes enclosed in a 

 gelatinous envelope ; and in due time this mass shapes itself into 

 a frustule resembling that of its parent, but of larger size. In 

 Epithemia (Fig. 122, A, b), however, — the first Diatom in which 

 the conjugating process was observed by Mr. Thwaites,* — the 

 endochrome of each of the conjugating frustules (c, d) appears to 

 divide at the time of its discharge into two halves ; each half 

 coalesces with half of the other endochrome ; and thus two Spo- 

 rangial frustules (e, f) are formed (as in certain Closteria, § 206, 

 note), which, as in the preceding case, become invested with a 

 gelatinous envelope, and gradually assume the form and markings 



Fig. 123. 



Self-Conjugation of Melosira Italica [Aulacoseira crenulata, 

 Thwaites) : — 1, simple filament ; 2, filament developing sporan- 

 gia ; a, b, c, successive stages in the formation of sporangia ; 

 3, embryonic frustules, in successive stages, a, b, c, of multipli- 

 cation. 



of the parent-frustules, but grow to a very much larger size, the 

 sporangial masses having obviously a power of self-increase up to 

 the time when their envelopes are consolidated. This doubling 

 of the Sporangial product of conjugation seems to be the ordinary 

 type of the process among the Diatoms. A curious departure 

 from the usual plan is observed in some of the filamentous species ; 

 for their component cells, instead of conjugating with those of 



* See "Annals of Natural History," Ser. 1, Vol. xx. (1847), pp. 9, 343, 

 and Ser. 2, Vol. i. (1848), p. 161. 



