ARANEAE. 37 



data that are afforded by ontogeny confirm our view, the embryo of 

 Galeodes closely resembling an Araneid embryo. More accurate 

 data as to the development of the Solifugae are very desirable. 



„ ,. VI. Araneae.* 



systematic : 



A. Tetrapneumones. 



Avicularia (Mygale), Atypus. 



B. Dipneumones. 



Epeira, Theridium, Agalena, Lycosa, and all the other 

 Araneae mentioned. 



Oviposition and the Constitution of the Egg. The Araneae 

 build nests or prepare cocoons for their eggs, and usually watch over 

 them. In many cases the cocoons are carried about by the mother, 

 held by the chelicerae {e.g., Dolomedes, Pisaura) or attached to the 

 abdomen {e.g., Lycosa, Tarantula). 



The eggs, which are rich in yolk, are surrounded by a vitelline 

 membrane as well as by an external envelope, probably secreted by 

 the oviduct, the latter being described as the chorion. A thin 

 protoplasmic layer (the periplasm or blastem) covers the yolk, which 

 in turn surrounds a central mass of protoplasm (the centroplasm), 

 within which the nucleus is situated ; from this central mass fine 

 protoplasmic strands extend to the surface, thus breaking up the 

 yolk into columns. 



Besides the nucleus, a remarkable structure is found in the eggs of 

 Araneae, and called the yolk-nucleus, but this is not yet sufficiently 

 understood. It consists of a compact accumulation of spherules ; 

 occasionally it is quite a complicated structure, composed of several 

 concentric layers. When the egg matures the yolk-nucleus usually 

 disappears, but it appears sometimes to be still retained, and is said 

 to be still found near the nucleus in one of the yolk -complexes 

 in the two- and four-celled stages of cleavage (Kishinouye). 



According to Ludwig (No. 66), the external envelope is marked out into 

 polygonal areas, but this has recently been referred to the breaking up of the 

 periplasm into polygonal divisions, Sabatier (No. 70) and Locy (No. 64), 

 these writers thus agreeing with older statements made by Balbiani (No. 46). 

 This polygonal marking must not be confounded with blastoderm-formation 

 (which only occurs later) ; the former is said to appear even before cleavage 



* [Pocock divides the Araneae into two groups — 



A. Mesothelae, comprising one genus, viz., Liphistius, with a segmented 



abdomen. 



■d r\ ■ ii u i ( Mygalomorphae. 



B. Opisthothelae J A / a ° chn0U10r p hae ._ ED . ] 



