File:The American Museum journal (c1900-(1918)) (17538952433).jpg

Title: The American Museum journal
Identifier: americanmuseumjo06amer (find matches)
Year: c1900-(1918) (c190s)
Authors: American Museum of Natural History
Subjects: Natural history
Publisher: New York : American Museum of Natural History
Contributing Library: American Museum of Natural History Library
Digitizing Sponsor: Biodiversity Heritage Library

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THE DEVELOPMENT OF A MOLL USE Z5 capsules, to the number of 50 or 60, each containing about 250 eggs, are united into a grape-like cluster generally found under the shell of the Crepidula attached to the stone or other object upon which it lives its sedentary life. The total number of eggs laid at one time by an animal is about 13,000. The unfertilized egg (Fig. a) is a nearly spherical single cell consisting of a very small amount of protoplasm surrounded by a relatively larger amount of yolk material, mostly in the form of small globules. Within the protoplasm, in a nearly central position, is found the nucleus of the cell. The whole egg is enveloped by a cell membrane.
Text Appearing After Image:
Fig. a The first change which takes place in the egg, preparatory to development, is a migration of the nucleus and protoplasm from a central position toward the upper surface of the egg, the yolk, or deutoplasm, taking its position below it. The egg thus be- comes distinctly symmetrical about a vertical axis (Fig. h). The upper pole, at which the protoplasm is found, is known as the animal pole; the opposite, or lower, as the vegetative pole, since ANIMAL POLE

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