Page:The New International Encyclopædia 1st ed. v. 18.djvu/512

* SPERMATOPHYTES. 440 SPEY, (ovule) and produces the female plant there. Tliis niegaspore vithin the ovule was once tiiought to be merely a sac-like cavitj', within which the embryo appeared, and hence was called the •embryo-sac'' (e. Fig. 1 ; s, Fig. 2). In germina- tion the megasjiore produces a female plant, with several or many cells, which has long been called 'endosperm,' and recognized as a prominent nutri- tive tissue within the seed. The female plant, therefore, is entirely inclosed within the ovule, and produces an egg (o, Fig. 1) which is reached by a pollen-tube {m, &g. 1) and fertilized. This act of fertilization is followed by two conspicuous results, namely (1) the development of the em- bryo (e. Fig. 2), and (2) the development of a hard superficial tissue (testa) in the outer part- of the ovulCj which hermetically seals the female plant and embryo within, the whole com- plex structure constituting the seed. In the seed condition the plant passes into a resting period of greater or less duration, and then, under favorable conditions, the seed is said to germinate. This simply means the renewed growth of the young plantlet, whose embryo, which had begun to develop, was checked by the hard investment of the seed. A seed, therefore, is a complex of three generations: (1) the old sexless generation (sporophyte), represented at least by the seed coats ; ( 2 ) the following female sexual "generation (gametophyte), represented by the endosperm; and (3) the new sexless genera- tion (sporophyte), represented by the embryo. SPERMATOZOON ( Neo-Lat., from Gk. (nri?p- ^a, sperma, seed + fvov, zoon, animal). The male germ cell. The phenomenon of sexuality consists of the union of two cells. In the lowest forms these may be alike, but in the higher plants and animals there is a difference in size of the two Uniting cells. The larger is called the female cell or 'egg,' the smaller the spermatozoiin. This difference in size is advan- tageous,' for it means a division of labor. The large cell is passive and accumulates a large amount of food-material by virtue of which the future embryo is better provided for. The sper- matozoon, on the other hand, retains the capacity for locomotion ; it seeks the passive egg. Conse- quently, the spermatozoon becomes as small as possible and is provided with a large locomotive organ — the tail, tlagellum, or lash. The spermato- zoon is thus a highly specialized, actively loco- motor cell. A typical flagellate spermatozoon consists of three parts: head, middle piece, and tail. The head contains the nucleus, made up of an extremely dense mass of chromatin ; also often an apical body or acrosome, lying in a spur of the head. The middle piece is larger than the tail and usually contains the eentrosome. Tlie tail is a cytoplasmic thread, containing a central delicate thread and having a lateral membrane or fin which makes the stroke of the tail more effective. Spermatozoa exhibit a great variety of forms. Thus, the head may be nearly globular or spear-shaped, or even of the shape of a cork- screw. The membrane may be absent or it may twist spirally around the axial thread. Finally the spermatozoon may, as in certain Crustacea, be not thread-like, but star-shaped or spindle- shaped, with the head at the centre. In plants, also, the spermatozoon (spermatozoid) exhibits a great diversity of form from a sphere to a ecrew-like thread. The spermatozoa develop in a special organ of the body called testis, typically a mass of germ cells, young and old. In the young male this gland is made up of epithelial cells known as primordial germ cells; from these by cell-division arise 'spermatogonia,' still undifferentiated cells. Tlie spermatogonia grow until they become very, big, and are then called 'spermatocytes.' Each large sperniatoc3'te divides and the daughter cells promptly divide again into 'spermatids,' four of which thus arise from each spermatocyte. But each spermatocyte has only half the number of chromosomes that the original spermatocyte had. Each spermatid now undergoes a change of form by «'hicli it becomes a spermatozoon, and not until then is it ready to fertilize the egg. See Fertilization. SPERMOPHILE (from Gk. airipiia, sperma, seed + (pt'Keiy, philein, to love). A ground- squirrel of the genus Spermophilus, of which more than a dozen species occur in the United States, but only one or two in Europe. They are all terrestrial, live in burrows under ground, feed chiefly on herbage and seeds, ' are very pro- lific, and are commonly called 'gophers' (q.v. ), thus confusing them with an entirely different group of mammals. Three of the species, at least, are sufficiently abundant to do much dam- age to lawns and cultivated fields. A very effec- tive means of destroying them is by soaking some absorbent substance in carbon bisulphide and placing it in the burrows. In size, form, color, and length and shape of tail, the spermophiles show great variety. They are usually some shade of brown, mottled, spotted, or striped with other shades. With the tail, they will average about a foot in length. All are western, and denizens of open regions, only two species occurring as far east as Illinois. The flesh is edible. Consult Bailey, "Prairie Ground Squirrels," in Bulletin -i (De- partment of Agriculture, Division of Ornithology and JIammalogy, Washington, 1893). Compare Chipmunk. SPERM WHALE. See Whale. SPES (Lat., hope). The Roman goddess of hope, represented as a youtliful divinity clad in a long robe and bearing a bud in one hand. Spes personified particularly hope for good harvests and for children, and gradually came to be looked upon as a goddess of the future, to be invoked at births, marriages, and other important times. SPETJSIP'PTJS (Lat, from Gk. S»reuVi7r7roi) (C.395-C.330 B.C.). An Athenian philosopher, nephew and pupil of Plato, with whom he is sup- posed to have visited Syracuse. For the last eight years of his life Speusippus was head of the Old Academy. He went even further than Plato in his mystical interest in the Pythagorean numbers, but in general agi'eed with his master. save that he denied the perfect goodness of the primordial unity, inasmuch as bad must be held to proceed from it as well as good. Consult Fischer, De Speusippi Atheniensis Vita (Rastatt, 1845). SPEY, spa. A river of Scotland, rising in rnverness-shire, and. after a northeast course of about 110 miles, falling into the Moray Firth, 3 miles west of Portgordon (Map: Scotland, E 2). The Spey is the second longest river in Scotland. It has salmon fisheries.