THE ARACHNIDA. i 429 
soft, leathery, and even transparent in texture, and capable of 
great extension, and this is the case in the true spiders whose 
abdomens are not in segments; but in the other family of the 
order, which includes the scorpions, and which have the abdomen 
articulated and formed of many segments, the skin, especially of 
the abdomen, is hard and solid. This last family allies the 
spiders to the Crustacea, and its members have not any spinning 
apparatus. The palpi are terminated by a pincer-shaped weapon, 
and the last segment of the abdomen is turned into a poison- 
bearing claw. The respiratory structures of the scorpion are much 
more elaborate than those of the ordinary pulmoniferous spiders, 
and a number of folds or lamin, attached above to a common 
tissue, are suspended side by side, like the leaves of a book, form 
the pulmonary branchia. Miiller says they can be distended 
with air, but probably it is necessary that they should always be 
kept slightly moist. These structures resemble somewhat those 
by which the land crabs and other terrestrial Crustacea breathe. 
The scorpions give birth to eggs which are hatched whilst passing 
from the mother, or shortly afterwards, and the little ones are 
frequently carried about by her until they have gained their full 
strength. The history of the growth and development of these 
ovo-viviparous Avachuida has, however, yet to be written. 
The common spider (Zegenxaria civilis) is remarkable for the 
number of its moults, and Mr. Blackwell has discovered that 
both sexes change their integument nine times before they arrive 
at maturity, once in the cocoon, and eight times after quitting it. 
He states that the life of the spiders lasts four years, and hints 
at the probability of the occurrence of parthenogenesis. 
Theridion lineatum, also a common spider, deposits about 170 
eggs, and leaves them in a silken cocoon, in which the young 
remain long after they are hatched, and are supplied with food 
by the mother; and Zheridion riparium watches over its young 
in the same manner, and feeds them with ants. 
Considering that the pulmoniferous spiders do not undergo 
any metamorphosis, and that the tracheary ones do, it is im- 
portant to settle the question whether anything like a progressive 
development resembling a metamorphosis goes on in the eggs of 
the first order. 
