History of infusoria, including the desmidiaceae and diatomaceae, British and foreign / by Andrew Pritchard.

  • Andrew Pritchard
Date:
1861
Catalogue details

Licence: Public Domain Mark

Credit: History of infusoria, including the desmidiaceae and diatomaceae, British and foreign / by Andrew Pritchard. Source: Wellcome Collection.

Provider: This material has been provided by Royal College of Physicians, London. The original may be consulted at Royal College of Physicians, London.

    84/1074 (page 64)
    tive body assumes the qmescent character which belongs to the seed of the higher plant, its vital function remaining dormant until circumstances favom- its further 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 suiTounding forms, and were obviously young frustules of the Cocconema. It would appear fi-om the figirres [appended to this account], that the production of the young frustules is preceded by the separation and throvnng off of the sLlicious 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. Hofraeister, iu the Eeports of the Saxony Natural History Society for 1857, and has been translated by Prof. Henfrey in the A. N. H. for January 1858. From, this we extract the following as supplementary to the previously-written history of the conjugation-process and of self-fission, as weL. of the Desmidieae (p.ll) as of the Diatomeae:— Conjugation is far more rarely met with in the Diatomeae than in the Desmidiese. It appears that this process occurs here only at particular epochs, differing according to the seasons, happening simultaneously in aU individuals, and quickly completed. Frequently as indications of conjugation having taken place have been met with (the occurrence of individuals of the same species, of remarkable diversity of size, side by side, in free Diatomeae, e. g. Pinnularia viridis, Surirella Ufrons, 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. Melosira, Podosira), 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 littie advanced by the observations of Focke (conjugation of Surirella), Griffith (conjugation of Navicula), W. Smith and Carter (conjugation of Cocconeis, Cymbella, Amphora). The following cases have been observed:— Formation of a single conjugation-cell, dividing veiy soon after its origin: in Himantidium pectorale, Cymbella Kutzingiaim, Cocco- neis Pediculus, Cocconeis Placentula, Oomphonema lanceolatum, Scliizonema Orevillii, Orthosira orichalcea, 0. Dickiei, remarkable from the repeated throw- ing-oflf of the coats of the conjugation-cell, the cracked halves of which clothed the conical ends of the conjugation-cell in shape of funnels; Orthosira va- rians, Surirella Ufrons, and a Navicula not speciacally determined. Here belongs also the only conjugation of a Diatomacean that I have seen, that of Cvclotella operailaia, conjugation-cells of which, mth adherent empty coats of the mother-ceUs, I found abundantly in ditches of a mai-shy meadow not far from Leipsic, in October 1852. They were not distingiushable m any essential respect from the Cyclotella Kiitzingiana figured by Thwaites. Next to these cases of the formation in the firat place of only one conju-