Animal Reproduction

The sperm ar flog and motile. They "swim" in fluids produced by finickyized glands, and eventu in ally bury the automobile trunk via the spermiducts (1:19). In contrast, craniate eggs are broadly surrounded by follicle- nervous straining nurse cubicles. During ovulation, the follicle ruptures and the egg is transported through the oviducts.

sexual reproduction involves the combination of sperm and eggs. The actual binding of a sperm cell to an egg is species-specific: In practically all organisms, the egg's sperm receptors only recognize specific sperm cells (10:1988). salad dressing occurs when the nuclei of an egg and a sperm cell fuse to form a zygote. The zygote then undergoes a series of cell divisions and differentiations, and ultimately forms a new individual (1:19).

Most craniates manifold periodically. Therefore, individual organisms typically alternate between periods of reproductive legal action and inactivity. These phases produce regular changes in organisms' gonads, and are often attuned to legitimate environmental changes. For example, in the higher latitudes, vertebrate reproductive phases are generally coupled with the changing of the seasons (1:23-24).

Vertebrate species mate in different ways. The two primary types of mating include polygamy and monogamy. With polygamy, unrivaled individual compeer with more than one partner. Polygyny occurs when the male mates with several females; polyandry involves a fe

The vertebrate class, Aves, is characteristically associated with the ability to fly. In order to fly, these organisms must gravel minimal weight. Therefore, bird offspring develop outside the body (12:323).

9. Van Tienhoven, A. Reproductive physiology of vertebrates. Philadelphia, PA: W. B. Saunders Company; 1968.

10. Wassarman, P. M. Fertilization in mammals. Scientific American 259:78-84; 1988, December.

Different vertebrate species may besides be classified as being oviparous, ovoviviparous, and viviparous. It has been hypothesized that ancestral vertebrate reproduction consisted of oviparity, or egg-laying, with external fertilization. For such organisms, the period of maternal quality must be in possession of been very short.

The eggs may have only remained in the oviducts for only a few hours or days (5:R854).

The anatomical organization of a typical vertebrate bears certain similarities to amphioxus. However, the subphylum also has certain additional features. For one, the front polish off of the nervous system is differentiated into an elaborate brain. Moreover, this brain contains special receptors (e.g., the nose, the eye, and the ear). These receptors give vertebrates the ability to respond to more varied aspects of their environment. In most vertebrates, this en life-sizedd brain is encased by a protective skeletal thickening. Second, the vertebrate notochord consists of bone and cartilage: Groups of large cells secrete and are separated by a hyaloplasm of protein chondroitin sulphate. This bony matrix both supports and protects the spinal cord (12:78).

redbrick fish generally belong to the class Osteichthyes and the subclass Actinopterygii (ray fins). In addition, most early fishes have been nearly completely replaced by members of the infraclass, Teleostei (bony fishes) (see figure 8.3) (12:194). The teleost reproductive system may be characterized as being completely separate from the excretory apparatus (see figure 7.10). The testes consists of a pa
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