638 AKACHNIDA. 



long enough to cross each other the jouited structure of the 

 limbs disappears, and they soon become divided into their 

 usual number of joints, tliough the tarsal joints are the last to 

 be perfected. At this time the maxillai become differentiated, 

 or split up, into the basal lobe and its appendage, or palpus. 

 Claparede compares the basal lobe to the coxa of the h'<>s, 

 though it is formed long before the coxje of the feet them- 

 selves. The anterior pair of appendages form the mandibles. 



The formation of the head is next in order. The "ceplialic 

 lobe" is divided into what the author calls two "procephalic 

 lobes," separated by a deep incision, and at tliis period the 

 head appears very distinct from the thorax. Afterwards the 

 anterior or ante-oral part of the head is, as in the case of the 

 "post- abdomen," folded back on the top, and then closely sol- 

 dered to the thorax, thus forming the so called "ceplialo- 

 thorax," Tliese procephalic lobes are sej^arated b}' a third 

 lobe or "triangular plate" which grows up between them, 

 forming the epichile. The mouth first appears as a longitu- 

 dinal farrow in this triangle, the posterior border of which 

 becomes the so called labium ("glossoide" of Latreille). The 

 labium thus originates in the spiders in an entirely different 

 way from the appendages, and is not formed, as Brulle sup- 

 posed, by the soldering of the maxilhe, hence we shall adopt 

 Latreille's term "glossoide" for this piece. 



Tlie two procephalic lobes afterwards unite, and are soldered 

 together on the median line, to form the anterior face of the 

 head. This approach takes place from above, over the buccal 

 frame (epichile). The numdibles are thus in advance of the 

 mouth, though primitively behind it. "The head is then in 

 the embryo of the spider very distinct from the thorax. Only 

 towards the end of embryonic life does the soldering of the 

 'cranium' and of the prothorax become so intimate that their 

 limits become indistinct. It is only from tliis moment that 

 there exists a true cephalothorax." (Claparede.) 



Towards the end of embryonic life the simple ej^es appear, 

 arising from four little furrows, called the "ophthalmic fur- 

 rows." Tliey are colored by the deposition of a small quantity 

 of pigment. They appear at an earlier i)oriod in the Acarina. 



Formation of the heart and viscera. After the walls of the 



