The growth of the brain : a study of the nervous system in relation to education / by Henry Herbert Donaldson.

  • Henry Herbert Donaldson
Date:
1909
Catalogue details

Licence: Public Domain Mark

Credit: The growth of the brain : a study of the nervous system in relation to education / by Henry Herbert Donaldson. Source: Wellcome Collection.

Provider: This material has been provided by the Augustus C. Long Health Sciences Library at Columbia University and Columbia University Libraries/Information Services, through the Medical Heritage Library. The original may be consulted at the the Augustus C. Long Health Sciences Library at Columbia University and Columbia University.

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    the eggs of the Lancclct, Amphioxus.^ In this simple fish it is possible to scj^aratc from one another the first two cells formed b\- the division of the egg. The cells thus obtained continue to develop and go through a number of stages characteristic of the normal eQ'^, but the larva is onh' half as large as the normal one, its component cells being reduced in size. This larva dies young, and whether it could be made to develop further is left for future experiment to decide. When the c^\^ has already formed four cells, it is still possible in the same manner to separate one of these, which will also A Q C roD Fig. 5.—Showing the egg of Ainphioxus in the one (A), two (13, and four cell (C) stages and below the corresponding larviu, a, b, c developed in each case from a single cell. The larva be- comes smaller as the fraction of ihc egg becomes less, X 135 diam. (Wilson.) develop alone, and give rise to a com[)lete larva, sa\'e that it is only one-quarter the normal size. This is still more difficult to rear (Fig. 5). During the past }'ear it has been shown (Morgan) that fragments of the unsegmented egg of the sea urchin may, when they contain both the male and feinale pronuclei, develoj) gastuhe, and this occurs even if nucleated fragments have but one-fiftieth ' WWsQW,/our/idl 0/ .][i>rp/ioloi^y, 1893.