The Life of Spiders 



the end of a narrow strip of cork; these pins are about one third 

 inch apart; by pressing these pins against a thread which it is 

 desired to photograph a section of the thread is obtained stretched 

 between the pins; thus mounted, the thread can be kept from 

 injury by contact with any object; the piece of cork bearing the 

 pins and silk is placed on the stage of a microscope so that the 

 silk is in front of the objective. It is now easy to study the silk; 

 and by combining the microscope with a camera in the ordinary 

 way, to make a photomicrograph of it. Figure 181 was made 

 from a photograph obtained in this way. 



II.— THE DEVELOPMENT OF SPIDERS 



The egg-sac— The eggs of spiders are laid in a mass and are 

 usually protected to a greater or less extent by a covering of silk, 

 the egg-sac or cocoon; but sometimes they are merely agglutinated 

 and are without a silken covering; this is the case in some of the 

 Pholcidae. 



Sometimes the egg-sac is so thin that it does not conceal the 

 eggs, being merely a loose web of threads; in other cases it is very 

 elaborate in structure. Several types of egg-sacs are discussed 

 later in the discussion of the motherhood of spiders. 



The life within the egg-sac. — As a rule the eggs hatch in a 

 comparatively short time after they are laid. The egg-shell is 

 broken, in the case of certain spiders at least, by a tooth on the 

 base of the pedipalps. Although the eggs hatch soon after they 

 are laid, the spiderlings may remain within the egg-sac for a long 

 time. Very many of the spiders living in the North pass the long 

 winter as spiderlings within the egg-sac. With these the eggs 

 are laid in the autumn, the spiderlings soon hatch, but remain 

 in the egg-sac till the following spring. Thus it may happen 

 that a spider whose entire life is one year in duration spends nearly 

 or quite one half of this period within the egg-sac. On the other 

 hand, the young of many species leave the egg-sac soon after 

 hatching. 



According to the observations of Dr. B. G. Wilder ('73a) 

 some of the young of Miranda aurantia feed upon their weaker 

 brothers and sisters; so that from an egg-sac that in early winter 

 contains a large number of spiderlings there emerge in the spring 

 a much smaller number of partly grown spiders. How general 



182 



