File:The doctrine of descent and Darwinism (1882) (14800224773).jpg

Identifier: doctrineofdescen1882schm (find matches)
Title: The doctrine of descent and Darwinism
Year: 1882 (1880s)
Authors: Schmidt, Dr. (Eduard Oskar), 1823-1886
Subjects: Evolution
Publisher: New York, D. Appleton
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library

View Book Page: Book Viewer
About This Book: Catalog Entry
View All Images: All Images From Book
Click here to view book online to see this illustration in context in a browseable online version of this book.

Text Appearing Before Image:
n a stalk,forms above its lower cross, gemmules which make theirappearance as spherical balls, gradually assume a bell-likeshape, and detach themselves on attaining the structureand form of a Medusa or sea-nettle. The Medusa (termedCladonema Radiatum, Fig. 3 B) is thus the offspring ofits utterly dissimilar parent, the Stauridium ; it repro-duces itself in the sexual method, and from its eggsproceed Stauridia. The two generations thus alter-nate; the cross-polype is an intermediate generation inthe development of the Medusa, so that the sexual genera-tion never originates directly from its egg. In the tape-worm, we have an illustration of the sameprocess, only in a somewhat more complicated form.It is known that from the intestinal canal of individuals ALTERNATE GENERATION. 43 afflicted with tape-worm, issue so-called somites or seg-ments of the tape-worm. These somites arc usuallyfilled with such an extraordinary number of ova thatthey seem like mere packets of eggs. It appears, how-
Text Appearing After Image:
FIG. 3. ever, from the evolutionary history of the tape-worm,and its relations with other annulosa, namely withleeches and Turbellaria, that notwithstanding their in-completeness and deficiency of organs, these somites areequivalent to sexually mature individuals ; or, accordingto Haeckels definition, are endowed with personality.If the tape-worm now comported itself like most otheranimals, somites would be directly developed from itseggs. But to this there is a very circuitous proceeding. 44 THE DOCTRINE OF DESCENT. If the egg of a tape-worm, by chance and good luck,strays into a congenial stomach,—for example, the eggof the human tape-worm, Toenia solium, into the stomachof a pig, the embryo wanders out of the stomach inwhich it quitted the egg, and makes its way into themuscles, where it swells out into a sort of cyst. Thiscyst is the first intermediate generation. It produces apeg-shaped gemmule, which, however, fails of its objectas long as the bladder worm, or Gargol, remains

Note About Images