B4 GENERAL HISTOEY OF THE INFT7S0EIA. 



tive body assumes the quiescent character wliich belongs to the seed of the 

 higher plant, its Yital function remaining dormant until circumstances favour 

 its furthei; development and the production of the young frustules of which 

 it is the destined parent. 



'^ In the gathering of Cocconema Cistula made in April 1852, which con- 

 tained numerous instances of the conjugating process, I observed the frequent 

 occurrence of cysts enclosing minute bodies, variable in their number and 

 size, and many of which had the outline and markings of the surrounding 

 forms, and were obviously young frustules of the Cocconema. It would appear 

 from the figui^es [appended to this account], that the production of the j^oung 

 frustules is preceded by the separation and throwing off of the silicious valves 

 of the sporangium, and the constriction or enlargement of its primordial 

 utricle, according to the number of young frustules originating in its pro- 

 toplasmic contents. In this gathering, forms of every size intermediate 

 between the minutest frustule in the cyst and the ordinary frustules engaged 

 in the conjugating process 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 re- 

 productive process." 



Since the preceding account of conjugation was written, a valuable, although 

 not a very lucid, contribution on the subject has appeared by Dr. Hofmeister, 

 in the Reports of the Saxony Natural Histor}^ Society for 1857, and has been 

 translated by Prof. Henfrey in the A. N. H. for January 1858. Prom this 

 we extract the following as supplementary to the previously-written history 

 of the conjugation-process and of self-fission, as well of the Desmidieae (p. 11) 

 as of the Diatomeae : — 



'' Conjugation is far more rarely met with in the Diatomeae than in the 

 Desmidieae. It appears that this process occurs here only at particular 

 epochs, differing according to the seasons, happening simultaneously in all 

 individuals, and quickly completed. Frequently as indications of conjugation 

 having taken place have been met with (the occuiTence of individuals of the 

 same species, of remarkable diversity of size, side by side, in free Diatomeae, 

 e. g. Pinnularia virklis, Surirella hifrons, Staurosigma lacustre, all the year 

 round, besides the occurrence of shorter or longer rows of cells of about 

 double the diameter, in the bands, of the forms remaining connected by the 

 lateral surfaces, e. g. Mehsira, Poclosira), yet it has seldom happened that 

 they have been met with in the moment of conjugation. 



" Since the classic researches of Thwaites upon this subject, the knowledge 

 of it has on the whole been but little advanced by the observations of Focke 

 (conjugation of Surirella)^ Griffith (conjugation of Navkida), W. Smith and 

 Carter (conjugation of Cocconeis, Cijmhella, Amphora). The following cases 

 have been observed : — " Formation of a single conjugation-ceU, dividing very 

 soon after its origin : in Himantidium pectorale, Cymhella Kiitzingiana, Cocco- 

 neis Pediculus, Cocconeis Placentida, Oomplionema lanceolatum, Schizonema 

 GreviUii, Orthosira oricJialcea, 0. DicTciei, remarkable from the repeated throw- 

 ing-off of the coats of the conjugation-ceU, the cracked halves of which clothed 

 the conical ends of the conjugation -cell in shape of funnels ; Orthosii^a va- 

 rians, Surirella hifrons, and a Navicida not specifically determined. Here 

 belongs also the only conjugation of a Diatomacean that I have seen, that of 

 Cyclotella operculata, conjugation- cells of which, with adherent empty coats 

 of the mother-ceUs, I found abundantly in ditches of a marshy meadow not 

 far from Leipsic, in October 1852. They were not distinguishable in any 

 essential respect fi^om the Cyclotella Kiitzingiana figured by Thwaites. 



" Next to these cases of the formation in the first place of only one conju- 



