. Comparative zoology, structural and systematic. For use in schools and colleges. Zoology. DEVELOPMENT. 207 Up into separate segments, which are, in fact, so many dis- tinct animals; and each turning over as it is set free, so as to bring the mouth below, develops into an adult Me- dusa, becoming more and more convex, and furnished with tentacles, circular canals, and other organs exactly like those of the progenitor that laid the original egg. Here we see a Medusa producing eggs which develop uito Infusoria-like larvas, and these grow into stationary. Fig. 174 Alternate Geueratiou: a, b, c,
. Comparative zoology, structural and systematic. For use in schools and colleges. Zoology. DEVELOPMENT. 207 Up into separate segments, which are, in fact, so many dis- tinct animals; and each turning over as it is set free, so as to bring the mouth below, develops into an adult Me- dusa, becoming more and more convex, and furnished with tentacles, circular canals, and other organs exactly like those of the progenitor that laid the original egg. Here we see a Medusa producing eggs which develop uito Infusoria-like larvas, and these grow into stationary. Fig. 174 Alternate Geueratiou: a, b, c, ova of an Acaleph (Chrysaora); d, e, /, Hy- dras ; g, h, Hydras with constrictions; i, Hydra undergoing fission; k, one of the separated segments, a free Medusa. forms resembling Hydras, The Hydras then produce not only Medusae by budding in the manner described, but also other Hydras like themselves by budding and by eggs. All these intermediate forms are transient' states of the Jelly-fish; but the metamorphoses can not be said to occur in the same individual. While a Caterpillar he- comes a Butterfly, this Hydra-like individual j^roduces a oiumher of Medusas. Alternate generation is almost con- fined to the low Kadiates (Fig. 190). 3. Growth and Repair. Growth is increase of bulk, as Development is increase of structure. It occurs whenever the process of repair exceeds that of waste, or when new material is added faster than the tissues are destroyed. Tliere is a specific. 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 Orton, James, 1830-1877. New York, Harper and brothers
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