THE ARACHNIDA. 
431 
mark off the cephalo-thoracic from the abdominal region. The 
integument may be seen to be forming in the abdomen, and the 
rudiments of the heart or dorsal blood vessel are noticed. The 
eyes begin to be distinguished. The diminution of bulk in front 
continues during the ninth period, and the division into two 
parts also. The chest and abdomen become more defined and 
elongated. The legs now present slight traces of a division 
into joints, and have increased greatly in size and length. 
Tenth period. The small end of the ovum, which is still 
more elongated, is now found to be distinguished from the large 
one by a true constriction dividing the ovum into two parts, 
denominated in the perfect spider, thorax and abdomen. The 
visible parts of the thorax are the mandibles, the palpi, and the 
legs. These latter appendages are folded upon the chest, and 
have grown so long as to cross the middle line of the body, 
and they are locked together like the fingers when the hands 
are clasped. The abdomen presents nothing remarkable except 
an elongated opaque streak, which exists along the middle of 
the under surface from the feet to the end of the belly. Heroldt 
considers this to be an indication of the development of the 
internal parts of the abdomen, of the intestinal canal, and the 
secreting organs. In proportion as the young spider increases, 
the external membrane or covering of the egg is applied more 
exactly to its body, and seems to represent an exterior skin, of 
which the young creature soon divests itself almost in the same 
manner as the caterpillar sheds the skin in which it is enveloped. 
By the increase of the young creature during this last stage 
of all, the membrane of the egg becomes so stretched, and is 
applied so exactly to the surface of the body, that the different 
parts of the body can be seen through it like the nymph or 
chrysalis of certain insects. The essential parts of the thorax 
are the head and feet. The head is of a white colour, and is 
surmounted by eight brown streaks ; the legs, which are also 
white, are closely applied to the chest, with their extremities 
alternating with each other. One may distinguish in each a hip, 
a thigh, a leg, and a tarsus. The articulations of the palpi and 
mandibles are also visible through the general envelope of the 
egg. The streak upon the abdomen has divided, and part of 
