110 AMERICAN SPIDERS AND THEIR SPINNINGWORK. 



tracheffi are shed, the broken parts of the old tube remaining among the 

 silk threads of the moulting frame, and all glands formed by ectoder- 

 mic invagination also lose their linings. 



The pharynx, oesophagus, and rectum take' part in the moult, as do 

 also the tendons, especially the muscles of the limbs, the matrix growing 

 around the old tendon and forming a new one, while the old one atrophies 

 and is cast away with the tegument. 



During moulting the number of spherical blood corpuscles, which usu- 

 ally is only three to four per cent, of the total number of corpuscles, 

 increases to ten per cent., almost all the red corpuscles being 

 'F^^ transformed into spheres. Want of movement during the process 



seems to be one but not the sole cause of this change in the 

 condition of the blood; and it must be remembered that a development 

 of all the internal parts of the body takes place at the moulting period, 

 so that the casting oif of the integuments, etc., is really but a secondary act. 

 In the last stages of development, when the embryonic cuticle is secreted, 

 according to Schimkevitch certain cells of the chitinogenous layer are aug- 

 mented in dimensions, taking a spherical form and dispersing themselves 

 under the chitinogenous layer, which forms above them something like a 

 raised vault above the cuticle. These are the future hairs. The nuclei of 

 these cells are of large size, but they are not very distinctly separated in con- 

 tour from environing cells. Some time thereafter these cells increase in size, 

 but their nuclei deviate proportionately less. These cells are already devel- 

 oped immediately under the cuticle ; it is evident that in growing 

 Moultmg y_^gy j^^^g pushed the chitinogenous cells against the sides. The 

 contours of the trichogenous cells deviate more apparently, and the 

 adjoining chitinogenous cells, from a contour ordinarily distinct, stretch out, 

 taking a semilunar form and investing by their sides the trichogenous 

 cells. The hair of spiders is a unicellular formation. ^ 



Mr. Wagner describes the origin of a new hair in detail. At a certain 

 epoch in the life of spiders more or less preceding the moult, according 

 to the various species, the inferior layer of the old skin, as we 

 Origin of ^^^^^ already seen, is retracted from the others, and the interval 

 Hairs ^^^^^ formed is filled with liquid. The retraction is effected 

 slowly. The sections made during that stage present the appear- 

 ance of Fig. 70. The inferior layer of the cuticle (in.lr.ct.o. Fig. 70) is 

 removed far from the other layers (ct.o), and the intervening space is filled 

 with liquid (Iq), which is so formed that it floats the tube which at the 

 time has served to form the primitive hairs. The position in which one 

 sees it in the figure is not the most common, but is quite rare; it is often 

 seen bent up in one fashion or another next the seat of the hair. 



1 W. Schimkevitch, " Materiaux pour la connaisance du developpment des Araign^es," 

 Memoirs Acad. Sci., St. Petersburg, 1886, Suppl. ant. LII., No. 5. 



