40 AMERICAN SPIDERS 



become differentiated into the chelicerae, palpi, and the legs. A 

 similar series appears on the abdominal portion, associated with a 

 rather definite segmentation of eight to twelve segments, but all 

 those behind the sixth true segment disappear as development pro- 

 ceeds. The basal pairs of buds persist for some time, and those of 

 the fourth and fifth segments develop into the paired spinnerets. 

 The buds on the second and third segments become invaginated 

 and go to form the book lungs. Finally, the embryo nearly encircles 

 the outside of the egg and the ventral surface is outside, unnaturally 

 bent and convex so it can lie within the stiff chorion. At this point 

 occurs what is called "reversion," a process by which the position 

 is reversed and the cephalothoracic portion becomes free. At about 

 this time too, with the pressure against the chorion of the expanding 

 embryo, and with the aid of a sharp egg tooth at the base of the 

 pedipalpi, the egg covering is broken. 



With the shedding of the chorion of the egg there is revealed a 

 creature somewhat spiderlike and yet obviously different from the 

 well-known spiderling. (The term "larva" has been applied to this 

 stage, but since that term more commonly describes insects at an 

 active feeding stage and has quite a different sense, it will not be 

 used here.) It is not unreasonable to suppose that this imperfect 

 creature is prematurely hatched, and that it actually represents part 

 of the egg stage. In order to gain space for fuller development and 

 more freedom, the tough chorion is broken but the creature is still 

 swathed in embryonal membranes. In mites an analogous stage is 

 called the deutovum, and is so similar to what exists in spiders that 

 the term may be applied to the latter also. 



This period in the spider's growth is not nearly so simple as 

 was once supposed. Dr. Ake Holm has discovered and described 

 in various Swedish spiders two or even more incomplete stadia (the 

 intervals between molts), each marked by the shedding of a mem- 

 brane. Some spiders hatch from the egg at a more advanced stage 

 than do others, the degree of development being roughly approxi- 

 mated by the specialization of the family. In Segestria, the first 

 postembryonal stadium brings to light a very primitive creature, 

 whereas in a more highly developed spider, such as Pardosa, the 

 deutovum is far more advanced. 



The deutovum is without dark coloration of any kind, the cara- 

 pace usually being milky white and the abdomen somewhat duller. 

 Tarsal claws are completely lacking on the pudgy legs. The crea- 

 ture is unable to feed or spin, for only parts of the important struc- 



