WEB-SPIDERS. 
221 
account of its function as a jaw, and the remaining five the palpus. The mandibles, 
too, are larger than in the Pedipalpi, and contain a poison-gland, opening at the tip 
of the second segment, which is transformed into a strong fang. In the abdomen, 
a marked character of most spiders is the absence of segmentation, its covering 
consisting of a soft, hairy integument, or a hard horny cuticle, while on its 
lower surface there are two pairs of shortened appendages, called the spinning 
mammilla}, upon which open the silk-glands. These mammillae are perhaps the 
most distinctive feature in spiders. Although varying considerably in shape and 
length, they are usually short and composed of two, or rarely three, segments. Each 
spinning appendage, however, is primarily 
composed of two branches, an outer and an 
inner, the outer forming the two- or three- 
jointed mammilla, while the inner branch 
or intermediate mammilla is always one- 
jointed. Consequently there may be as 
many as eight mammillae; usually, however, 
there are but six, owing to the disappear¬ 
ance of the inner branches of the first pair 
of spinning appendages. 
The oldest known form (. Arthrolycosa) 
of the Carboniferous, differs from nearly all 
existing forms in having the abdomen pro¬ 
tected above by a series of plates, as in the 
recent genus Liphistius, to which it was 
doubtless allied. In Tertiary times, spiders 
closely related to those now existing were 
abundantly distributed over the Northern 
Hemisphere, as their well preserved remains 
from the Oligocene amber beds of the Baltic 
and from the gypsum beds of Aix satis¬ 
factorily testify. 
The females of all spiders lay eggs, from 
which the young are subsequently hatched, 
laying, is to spin a small and often saucer - shaped web. In this the eggs are 
deposited, and are then covered over with two layers of silk forming a cocoon. The 
cocoons differ greatly in shape and colour and texture, according to the spider that 
makes them. They may be green, yellow, white, mottled, or nearly black; round, 
oval, lenticular, or cigar-shaped; soft and woolly, hard and nut-like, or smooth 
like parchment; while the outer casing is sometimes caked with earth or other 
foreign material for purposes of concealment. After the construction of the cocoon, 
the mother’s interest in its fate varies in different spiders. Sometimes she pays 
no further attention to it, as in the case of the garden spider ( Araneus ), which 
suspends it in or near her web, and leaves the young to shift for themselves. 
In some cases, again, she remains for a longer or shorter time on guard in its 
vicinity, sometimes spinning a regular nest for her young and herself during this 
period of quiescence; but in other cases, especially among the wandering species, 
ANATOMY OF COMMON CROSS SPIDER (ArCineus 
diadema). 
1, Foot with claws and hairs ; 2, Mandible with 
poison-gland and duct; 3, Faceand jaws ; 4, Spin¬ 
ning mammillae; 5, One of the spinning papillae. 
The first act of the mother before 
