282 THE MICROSCOPE. 



In the family Maiada, or sea-spiders, the carapace is more or less 

 narrowed in front, forming a projecting beak or rostrum the legs are 

 long and hairy ; the back covered with spines and hairs, much resem- 

 bling some spiders, whence the name of spider-crabs or sea-spiders, by 

 which these animals are known. 



Arachnidce. The animals forming the class Arachnida, which in- 

 cludes the spiders and their allies, are amongst those which are viewed 

 with disgust and aversion by the generality of mankind. Confounded, 

 in the popular mind, with the reptiles, they of course come in for 

 their share of the bad reputation of those creatures, and some of them, 

 no doubt, not without reason ; but on a closer examination we find 

 that, however unattractive they may be in appearance, they present 

 much that is interesting both in their structure and habits. 



They are distinguished from the other Arthropoda by their aerial 

 respiration, their possession of four pairs of legs attached to the ante- 

 rior division of the body, and the total absence of antennae. The body 

 is usually covered with a softish skin, which, however, sometimes attains 

 a horny consistency. In the lower forms, the division of the body into 

 separate regions is quite unrecognisable, and the whole forms a roundish 

 or oval mass, which does not even present traces of segmentation. In 

 the higher groups the body is composed of two principal divisions, of 

 which the anterior, as in the Crustacea, consists of the thoracic seg- 

 ments, amalgamated with those of the head, and forming together a 

 mass called the cephalothorax. In the highest forms the division of 

 the thorax into separate segments becomes apparent ; but the anterior 

 segment is still amalgamated with the head. The structure of the 

 abdomen varies greatly. In some cases it forms a soft round mass, 

 without any traces of segmentation j whilst in others, as the scorpions, 

 it is produced into a long flexible jointed tail. 



The Arachnida are divided into two orders : Tracliearia and Pul- 

 monaria. The first includes the Acaridce or Mites, in which there are 

 tracheae, as in insects, but no distinct vascular apparatus : in the 

 second, which includes spiders and scorpions, there are pulmonary 

 cavities, and a well-developed circulating system. 



Of spiders, the diadem (Epeira diad&ma) is one of the largest of the 

 British species ; it is a garden spider, and is easily recognised by the 

 beautiful little gem-like marks on its body and legs. Spiders abound 

 on every shrub ; and when we consider that the spider is destitute of a 

 distinct head, without horns, one-half of its body attached to the other 

 by a very slender connection, and so soft as not to bear the least pres- 

 sure, its limbs so slightly attached to its body that they fall off at a 



