Handbook of field and general ornithology; a manual of the structure and classification of birds (1890) (14563556797)

Identifier: handbookoffieldg00coue (find matches)

Title: Handbook of field and general ornithology; a manual of the structure and classification of birds

Year: 1890 (1890s)

Authors: Coues, Elliott, 1842-1899

Subjects: Birds -- Collection and preservation Birds -- Classification Birds -- Anatomy

Publisher: London, Macmillan

Contributing Library: American Museum of Natural History Library

Digitizing Sponsor: Biodiversity Heritage Library

Text Appearing Before Image:

d in the germinative process. Recurring to the femaleDynamanuela, consisting of granular protoplasm (vitellus) includedin its cell-wall (vitelline membrane) and including its nucleus andnucleolus (germinal vesicle and germinal spot), we will trace it upto the time it begins to take shajse as an embryo chick. At first, 332 GENERAL ORNITHOLOGY as I have observed before, it is like any other amoiba; the first stepof development is probably a retrograde one; for if there ensues,when the spermatozoa melt into the ovum, the result affirmed formammalian ova, the original germinal vesicle and germinal spotdisappear, and the Avhole content of the ovum proper is simply ahomogeneous mass of granular protoplasm. In this retrograde step,the organism, at the lowest possible round of the ladder of evolu-tion, is called a monerula. The germinal vesicle and spot, however,are speedily reconstructed, and the ovum looks precisely as it didbefore. But observe that the actual difference is enormous; for it

Text Appearing After Image:

Fig. 111.—Segmentation of the vitellus by discoidal cleavage, diagrammatic, x about 10 times,after Haeckel. Only the tread, cicatricle, or germ-yelk (Pigs. 109, b, 110, A) is represented,as no other part of the whole yelk-ball undergoes the process. A, separation into 2 ; B, into 4 ;C, into 16, by 8 radial and 1 concentric furrow ; D, into many parts, by 16 radial and about 4concentric furrows ; E, 64 radial and about 6 concentric furrows ; F, the whole tread broken upInto a mulberry-mass 0norula) of cells. now consists of the blended substance of the original ovum and ofthe spermatozoa; and in this duplex or bisexed state, before anyfurther step is taken, the creature is called a cytula,—the parentcell of the entire future organism. In the former state it couldreproduce nothing, not even itself ; for it is the strange physiologicallaw of a Dijnamamccha that it cannot reproduce like an ordinarycell, but must evolve an entire organism, like both of those two whosevital forces it co

1890 Bücher elliott coues Buchillustrationen Vogelkunde Vögel Zoologische Illustration Naturgeschichte Zoologie Amerikanisches Museum für Naturgeschichte Bilder aus dem Internetarchiv

1890

American Museum of Natural History Library

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