. A manual of zoology. ss MANUAL OF ZOOLOGY multiplication also assumes the form in some cases of a process of production of internal buds in the shape of groups of cells called gemmules, which eventually become detached and develop into new individuals. In the fresh- water sponges {SpongiUidw) multiplication takes place very actively by means of such gemmules, each of which is a spnerical group of cells enclosed in an envelope composed of peculiarly shaped siliceous spicules, termed amphidiscs (Fig. 40, right side). All sponges multiply by a sexual process — by means of male cells, or sperms,
. A manual of zoology. ss MANUAL OF ZOOLOGY multiplication also assumes the form in some cases of a process of production of internal buds in the shape of groups of cells called gemmules, which eventually become detached and develop into new individuals. In the fresh- water sponges {SpongiUidw) multiplication takes place very actively by means of such gemmules, each of which is a spnerical group of cells enclosed in an envelope composed of peculiarly shaped siliceous spicules, termed amphidiscs (Fig. 40, right side). All sponges multiply by a sexual process — by means of male cells, or sperms, and female. rT@ x Fig. 40. — Various forms of sponge spicules. (From Lang's Text-Book.} cells, or ova. Ova and sperms are developed in the same sponge, but rarely at the same time. The cell destined to form sperms divides into a number of small cells, giving rise to a rounded mass of sperms. The latter, when mature, have oval or pear-shaped heads and a long taper- ing appendage or tail. Each cell destined to form an ovum enlarges, and eventually assumes a spherical form. After a sperm has penetrated into its interior and effected impreg- nation, it usually becomes enclosed in a brood-capsule formed for it by certain neighbouring cells, and in this situation, still enclosed in the parent sponge, it undergoes. 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 Parker, T. Jeffery (Thomas Jeffery), 1850-1897; Haswell, William A. (William Aitcheson), 1854-1925. New York, The Macmillan Company; London, Macmillan & Co. ,Ltd.
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