434 ARACHNIDA—CHERNETIDEA CHAP. 
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 the 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 
1 See Bernard, J. Linn. Soc. xxiv. (Zool.), 1893, p. 422. 
