THE ARACHNIDA. 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 laminae, attached above to a common 

 tissue, are suspended side by side, like the leaves of a book, form 

 the pulmonary branchia. Muller 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-vivi parous Arachnida has, however, yet to be written. 



The common spider {Tcgcnaria 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 Theridion ripariiun 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. 



