566 CLASS ix. 



separated from the yolk, afterwards lies between two lateral portions 

 of the yolk, which, by transverse indentations, change into coccal 

 sacs placed in pairs. These sacs, in connexion with the intestinal 

 canal, are the rudiments of the biliary vessels and of the liver. The 

 yolk changes into the liver, or the so-called adipose body. The 

 limbs arise as conical appendages placed under the ventral surface, 

 with the extremities turned downwards towards each other. On 

 the dorsal surface of the yolk is seen a streak running longitudi- 

 nally as the rudiment of the heart, that is at first without vessels. 

 The nervous system, in its central parts, is formed at a still earlier 

 period, and the cerebral ganglion is in the beginning proportionally 

 much larger than it is afterwards 1 . 



We have already said that the scorpions are viviparous. With 

 the egg-laying spiders, the egg, under the changes of development, 

 slowly loses its previous form, and almost assumes that of a spider, 

 indicating all the external parts of the inclosed animal. At length 

 the shell bursts on the thorax, and the spider, first with the head, 

 and afterwards with the thorax, comes to view ; then follows the 

 abdomen, to which however the egg-membrane, like a scale, con- 

 tinues attached for a time ; then come the feelers and feet 2 . The 

 young spider, through whose integument the granules of the yolk 

 may be clearly distinguished, is not yet in a state to weave a web 

 and catch its prey ; for the spinning organs are still concealed be- 

 neath the common integument. After the lapse of a week, or, in 

 some species, a longer time, during which the spider takes no food, 

 it casts its skin for the first time, and is, as it were, born for the 

 second time. The young spiders now quit, on some mild clay in 

 May or June, the web in which the mother had hidden her eggs ; 

 they allow themselves to fall on the ground by a thread, and begin 

 at once to weave their nets, or in some other way, according to the 

 instinct of their kind, to watch for small insects corresponding to 

 their age and powers. 



1 On the development of spiders see M. HEROLD De Generatione Aranearum in Ovo, 

 Marburgi, 1824, fol. cum tab. seneis: DE WITTICH Observations de Aranearum ex ovo 

 evolutione, Hallse, 1845; f scorpions, H. RATHKE Zur Morphologic, Riga u. Leipzig, 

 1837. 4to. pp. 17 34. PI. I. figs, i TI ; compare also the shorter description of these 

 last observations and of those of HEROLD in BDRDACH Die Physiologie als Erfarumjs- 

 wissensckaft, 7te Ausg. n. 1837. s. 242 248. 



2 DE GEEB Mem. pour servir a I' Hist, des Ins. vii. pp. 195, 196, PI. 18, figs. 

 1114. 



