108 



NATURAL HISTORY OF ARTHROPODS. 



saved the trouble of gnawing their way out. The young of Micaria cut a smooth, 

 round hole in their paper-like cocoon just large enough for them to come out one 

 by one. 



The fertilization of the eggs takes place when they have reached their full size and 

 are about to be laid. After the eggs are laid it is very easy to watch their develop- 

 ment. They grow just as well anywhere else as in the cocoon, and, in order to see 

 through the shell, it is only necessary to cover the egg to be examined with oil, alcohol, 

 or any liquid that will wet it. The rate of growth varies according to circumstances. 



abed 

 Fig. 152. — Segmentation of spider*s eggs. «. Before segmentation. 6, c, d. Three stages of division. 



Some eggs laid in autumn develop slowly all winter, while others laid in summer are 

 ready to hatch in a fortnight. The segmentation is regular, but from the relations of 

 the protoplasm and yolk we do not find the regular segmentation spheres so common 

 in most forms, but in their stead beautifully-irregular cleavage cells, which are shown 

 in the adjacent figures. 



In about four or five days the young of the long-legged cellar spider becomes 

 lengthened out into a sort of barrel shape, and six whitish rings run half way round it, 

 on each of which appears soon after a pair of little knobs, one each side. These are 

 the six segments of the thorax, and the six pairs of limbs, and their gradual growth is 

 shown in Fig. 153, a to d. At first there is no sign of a head or abdomen ; but shortly 



Fi&. 153. — Later stages of spider's eggs. a. Division into segments. 6. Appearance of legs, 

 of abdomen and abdominal legs. d. JJearly ready to hatch. 



Formation 



after there appears an opaque knob at one end, under which is a pair of little knobs, 

 such as appeared at first on the thoracic segments ; then appear two pairs, then three, 

 and so on, till there are six pairs, which mark tlie six segments of the abdomen. Up 

 to this time the embryo has been rolled up with the under-side outward, but now it 

 begins to turn, and in a day or two has its back outward. The constriction between 

 the thorax and abdomen begins about' this time, and in a few days more the spider is 

 ready to hatch, Fig. 153, d. 



The hatching occupies a day or two. The shell, or rather skin, cracks along the 

 lines between the legs and comes off in rags, and the spider slowly stretches itself and 

 creeps about. It is now pale and soft, and without any hairs or spines, and only small 

 claws on its feet ; but in a few days it gets rid of another skin, and now begins to look 



