S P E 



[411 ] 



S P I 



E. Forbes placed it at or below 

 the base of the Lower Greensaud. 



SPECULAR, (speculum, Lat. a mirror.) 

 Any body which presents a smooth 

 and brilliant surface, and which 

 reflects light. 



SPHAGO'DUS. (slaughtering or mur- 

 dering tooth, from ff^aryrj and oSovs 

 Gr.) The name given by M. 

 Agassiz to a genus of ichthyolites 

 found in the Tipper Ludlow rocks. 



SPHA'GNUM PALTJ'STRE. A species of 

 moss, generally constituting a large 

 portion of the entire mass of peat 

 bogs. The sphagnum palustre has 

 the property of throwing up new 

 shoots in its upper part, while its 

 lower part decays, and from this 

 circumstance it mainly contributes 

 to the formation of beds of peat. 



SPHERE, (sphc&ra, Lat. o-0a?/>a, Gr.) 

 A solid, generated by the revolu- 

 tion of a semicircle abont its dia- 

 meter, which remains fixed; a 

 globe ; an orbicular body ; a body 

 of which the centre is at the same 

 distance from every point of the 

 circumference; such a solid body 

 that all lines drawn from its centre 

 to its surface are equal. The lines 

 are called radii. 



SPHE'RICAL. (sjpherique, Pr. sferico, 

 It.) Round; orbicular; globular; 

 Having all its diameters equal. 



SPHERI'CITY. Roundness; globosity. 



SPHE'ROID. (from afia'ipa, a sphere, 

 and etdoe, likeness, Gr.) A solid 

 body approaching to the form of a 

 sphere. A spheroid may be either 

 oblate or prolate ; an oblato sphe- 

 roid resembles an orange, having 

 its poles flattened, such is the form 

 of the earth and planets ; a prolate 

 spheroid has its poles drawn out, 

 and its form somewhat resembles 

 an egg. 



SPHERO'IDAL. Having the form of a 

 spheroid, whether oblate or prolate. 



SPHENO'PTERIS. A very beautiful and 

 delicate subgenus of fossil ferns or 

 filicites, described by Brongniart. 



SPHE'RTJLE. (spharula, Lat.) A little 

 globe ; a globule. 



SPHI'NCTER. (from <r0/7<yw, Gr. to 

 contract.) The name given to 

 certain muscles whose office it is to 

 contract the part in all directions, 

 drawing it together as the mouth 

 of a purse is contracted by a cir- 

 cular string. 



SPI'DER. The different species of spi- 

 ders compose the genus Aranea, or- 

 der Pulmonariae, class Arachnides. 

 The male spider possesses four pairs 

 of legs, the female five, the addi- 

 tional pair enabling her to carry 

 her eggs. The legs are composed 

 of seven joints, the two first form- 

 ing the hip, the third the thigh, 

 the fourth and fifth the tibia, the 

 sixth and seventh the tarsus. The 

 feet are spread out in diverging 

 rays, so as to include a wide circle, 

 and afford an extensive base of 

 support ; they terminate in two, 

 or, sometimes, in three hooks. In 

 front of the head are placed mem- 

 bers resembling feet, having affixed 

 to them, or terminating in, a move- 

 able hook, or pincers, flexed infe- 

 riorly, underneath which is a mi- 

 nute opening that permits exit to 

 a venomous fluid contained in an 

 adjoining gland. By the injection 

 of this poisonous fluid the common 

 spider of this country is able to kill 

 a fly in a few minutes, and the 

 large spider of South America can, 

 by the same means, destroy the 

 smaller vertebrated animals, and 

 produce, even in man, severe con- 

 stitutional disturbance. The greater 

 number of species possess a curious 

 apparatus for spinning threads, and 

 for constructing nets, for the entan- 

 glement of flies and small insects. 

 This net, or web, is as various as 

 the species, each species construct- 

 ing its own peculiar form of net; 

 in addition to the principal web, 

 which is spun out for the capture 

 of small insects, the spider fre- 

 quently constructs a smaller one, 



