434 ARACHNIDA CHERNETIDEA ( hap. 



The alimentary canal dilates into a small sucking pharynx before 

 passing through the nerve-mass into the large many-lobed stomach, 

 but the narrow intestine which terminates the canal is convoluted 

 or looped, and possesses a feebly -developed stercoral pocket. 



Above the stomach are situated the spinning glands, the 

 products of which pass, by seven or more tubules, to the orifice 

 already mentioned on the distal joint of the chelicerae. The 

 abdominal or cement-glands are in the anterior ventral portion 

 of the abdomen. No Malpighian tubes have been found. 



The tracheae from the anterior stigmata are directed forward; 

 those from the posterior stigmata backward. Bernard ^ has found 

 rudimentary stigmata on the remaining abdominal segments. 



The heart is the usual dorsal tube, situated rather far forward, 

 and probably possessing only one pair of ostia. The nerve-cord 

 is a double series of ventral masses, united by transverse com- 

 missures. These undergo great concentration in the last stages 

 of development, but in tlie newly-hatched Chernetid a cerebral 

 mass and five pairs of post-oesophageal ganglia can be distinguished. 

 There are two peculiar eversible " ram's-horn organs," opening 

 near the genital opening. They are said to be present only in 

 the male, and have been taken for the male organs, though other 

 writers consider them to be tracheal in function. 



Development. — Some points of peculiar interest are pre- 

 sented by the embryology of these animals, the most striking 

 facts being, first, that the whole of the egg is, in some cases at 

 all events, involved in the segmentation ; and, secondly, that there 

 is a true metamorphosis, though the larva is not free-living, but 

 remains enclosed with others in a sac attached to the mother. 



At the beginning of winter the female immures herself in a 

 silken retreat, her body distended with eggs and accumulated 

 nourishment. About February the egg-laying commences, thirty 

 eggs, perhaps, being extruded. They are not, however, separated 

 from the mother, but remain enclosed in a sac attached to the 

 genital aperture, and able, therefore, to receive the nutritive fluids 

 which she continues to supply throughout the whole period of 

 development. 



The eggs, which line the periphery of the sac, develop into 

 embryos which presently become larvae, that is to say, instead 

 of further development at the expense of yolk-cells contained 

 ^ See Bernard, J. Linn. Soc. xxiv. (Zoo!.), 1893, p. 422. 



