Identifier: firstprincipleso00herb (
find matches)Title:
The first principles of heredity; with 75 illustrations and diagrmsYear:
1910 (
1910s)Authors:
Herbert, S. (Solomon), b. 1874Subjects:
HeredityPublisher:
London, A. and C. BlackContributing Library:
NCSU LibrariesDigitizing Sponsor:
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view book online to see this illustration in context in a browseable online version of this book.Text Appearing Before Image:Viridis. (From Claus, Textbook of Zoology.) a and 6, free, swimming, in different states of contraction; c to e,encysted and in process of division. cells may already be called germs in the proper sense, butthey differ from the real germ-cells in this respect—thatthey are sexless. Sporulation is chiefly to be found among the lower plants—Algae, Mosses, Ferns, etc.—and in a few kinds of Protozoa.In some cases—as, e.g., in the Infusorian Euglena—thewhole contents of the original organism, after becomingencysted, break up into a mass of spores, which, burstingthe mother-shell, swarm freely about as the new youngindividuals. REPRODUCTION 17 B. Conjugation. Conjugation, which means the union of two separateindividuals for the purpose of propagation, gives us thetrue connecting-hnk between asexual and sexual repro-duction. The transition between them is very gradual—somuch so that we may trace every stage from the union oftwo organisms completely alike in every respect up to theText Appearing After Image:Fig. 10.—Conjugation of Noctiluca. (After Ischikawa.) (From Weismann, The Evolution Theory.) A, two individuals coalescing; B, fusion of cells; C, beginning ofdivision ; D, completion of division ; pr, protoplasm ; K, nucleus ;G, cell-body ; CK, centrosome. true sexual mating of distinct male and female in thehigher animals. We have, to begin with, two (or rarely more) individualsof the species (as in Algae or Infusorians) simply minglingtheir combined bodies into one, and thereafter multiplyingby simple division in the ordinary manner. In the Bell-animalcule (Vorticella), mentioned once before, conjugationtakes place between the large mother-animal and one ofthe much smaller progeny, which has resulted from re- 3 iS THE FIRST PRINCIPLES OF HEREDITY peated divisions (see Fig. 4, c); in the Alga Zanardiniathe two conjugating cells are already of widely divergentcharacter, approaching in type the bulky female and minuteactive male germ. Further, that conjugation means more than mere fNote About Images Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original work.