A history of Infusoria : including the Dismidiaceoe and Diatomaceoe, British and foreign / by Andrew Pritchard.

Date:
1861
Catalogue details

Licence: Public Domain Mark

Credit: A history of Infusoria : including the Dismidiaceoe and Diatomaceoe, British and foreign / by Andrew Pritchard. Source: Wellcome Collection.

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

    33/1068 (page 17)
    thinner, as if giving way at that spot. On the thii-d morning the membrane had broken and the grannies escaped, leaving the neai-ly emptied case (I. 12). Inasmuch as a sporangium may pass successively from a smooth to a spinous condition, it follows that the transitional stages of one species may be mistaken for the final stage of another; hence a difficulty in determining to what plant detached scattered sporangia may belong. It is only, indeed, when these seed- capsides occui- in company with the fronds producing them that we axe enabled to pronounce decisively by what species they are generated. As the foregoing account of conjugation and sporangia passed through the press, we met with the valuable paper of Dr. Hofmeister on the propagation of the DesmidieiE and Diatomese, translated by Prof. Henfi-ey from the Report of the Natural Histortj Society of Sa^vony for 1857. This commu- nication tends to clear up the questions of the nature of the sporangia and of the relation of theii- contents to the propagative process. The conciseness of the description renders abridgment undesirable; and we accordingly present it (so far as it relates to the points in question) as it stands in the Annals of Natural History (1858, i. p. 2) :— The conjugated individuals of Cosmarium tetraopMialmum displayed exactly the behaviour which EaLfs has represented and Braim described of those of Cosmarium margaritiferum. The Cosmaria which had commenced the conjugation process appeared cracked apart at the constricted place in the middle. Into each of the halves of the tuberculated ceU-coat of the two mother-individuals extended a continuation of the membrane of the conju- gation-ceU. This smooth membrane completely lined the interior of the tuberculated half-sheUs. The contents of the conjugation-cell revealed no definite aiTangement; they were mostly accumulated in the middle into an irregularly-shaped ball; in other cases separated into several such balls, part of which extended even into the split half-sheUs of the mother-cell. With these conjugated individuals, in the same fluid, occuiTed (veiy spaiingly) par- ticular specimens which bore, in the middle space between the two separated half-shells, a broad, delicate-waUed utricle, the circumference of which about equalled that of the two half-ceUs taken together. The arrangement of the ceU-contents in the primary portions of the cell did not appear essentially altered; the contents of the intermediate expansion consisted of a thick coat upon the wall of granular protoplasm Avith sparingly-scattered chlorophyll. This condition is probably that which immediately precedes conjugation, originating by excretion of new cellulose at the deepest part of the constric- tion, after the cracking of the membrane and separation of the primaiy halves of the cell, exactly as in normal cell-division, from which this process can only be distinguished by the omission of the formation of a septum at the narrowest part of the isthmus. Similar phenomena have been observed by Nageli in Cosmarium crenulatum, and by Mrs. Herbert Thomas in Cosmarium margaritiferum (scarcely specifically distinct from C. tetraoplithalmwn^, only that here the intermediate piece of the Alga did not conjugate Anth the similar piece of another individual, but, producing tubercles on its outer surface, continued the vegetative life. In other conjugation-cells there lay, in the middle part of the eonjugation- ceU, a globular cell enveloped in a rather thick membrane, of gelatinous aspect, and smooth on the outside (the spore). No intermediate stages could be found between this and the previously-described condition. Experiments, in which an attempt was made to obtain a completion of the less-advanced conjugation under the microscope, all failed. Apparently the conjugation- cell is exceedingly sensitive to any external injury, especially to contact vAt\\ 0