Arachnida and Myriapoda. 31 



EXTERNAL FEATURES OF THE SPIDER. 



Spiders are best preserved in alcohol, as they shrink in drying. 



1. The anterior division of the body is the cephalothorax, 

 or united head and thorax. 



2. The large posterior division is the abdomen. 



3. How many legs are there? To what are they attached? 

 How many segments are there in each ? Examine the feet under 

 a microscope. Make a drawing of one of the feet. Can a spider 

 climb out of a tumbler? Compare it with the beetle in this 

 respect. 



4. With a dissecting needle pry apart the mandibles, at the 

 front of the head. The duct of the poison gland opens at the 

 tip of each mandible. 



5. Back of the mandibles find a pair of small jaws, the maxillae. 



6. To the maxillae are attached a pair of jointed appendages, 

 resembling a pair of legs, the maxillary palps. 



7. With a lens look for the simple eyes above the jaws. How 

 many are there, and how are they arranged ? 



8. With a lens examine the spinnerets at the posterior end of 

 the abdomen. With a pair of forceps hold a live spider by one 

 leg, and watch the beginning of spinning. 



9. Besides air tubes, some spiders have one or two pairs of lung 

 sacs, composed of several leaves, into which blood flows, and is 

 thus aerated. 



Place the description of the spider alongside the list of charac- 

 ters common to insects, and note what features are common to the 

 spider and all the insects ; also the points wherein they differ. 

 Spiders belong to the class Arachnida. 



Read Emerton's Spiders, their Structure and Habits. 



MYRIAPODS. 



One form of " thousand legs," commonly found under stones 

 and under the bark of dead stumps and logs, is well known by its 

 cylindrical body, by its numerous, short, hairlike feet, and by its 



