DEVELOPMENT OF THE EXTERNAL FORM OF THE BODY. 



51 



Ae<t. 



Fig. 27. — Embryo of an Araneid (spl) showing the 

 dorsal curvature of the germ-band and the rudi- 

 ments of the abdominal limbs (original). ch, 

 chelicerae ; d, yolk ; U, cephalic lobe ; ped, pedi- 

 palps; j' 1 -p 4 , ambulatory limbs; 1-7, abdominal 

 segments, the provisional limbs being visible on 

 the first five ; si, caudal lobe. 



(sp 1), of the presence of a first abdominal segment (Fig. 27, 1), which 

 is quite as distinct as the following segments, and shows indications 

 of a pair of abdominal 

 limbs.* In Agale?ia also, 

 which has been repeatedly 

 examined, this segment 

 is found, and the em- 

 bryo, at a stage nearly 

 corresponding to that il- 

 lustrated in Fig. 27, 

 shows indications of the 

 rudiments of a pair of 

 limbs. These rudiments 

 are but slightly developed 

 in Agalena (less so than 

 in Fig. 27), and soon 

 completely disappear. A 

 similar condition of this 

 first abdominal segment 

 is found in other Araneids 

 (Korschelt). 



The first abdominal appendage is followed by others, varying in 

 number from two to five, but usually by four, similar to those already 

 described, and, finally, a much less distinct appendage seemed to be 

 recognisable on the sixth segment in the form illustrated in Fig. 27. 

 We should not have laid any stress upon this, as the sixth appendage 

 was not sufficiently distinct, had it not been evident from Claparede's 

 and Emerton's figures that in other Araneids ( Clubiona and Pholcus) 

 the sixth provisional pair of limbs is quite distinct. The appearance 

 of six pairs of abdominal limbs is of importance in establishing great 

 similarity between the Araneae and the Scorpiones. This similarity 

 is specially seen in the further fate of the provisional limbs (p. 57). 



The first abdominal segment" seems, in many species, to undergo degeneration 

 early. Nothing can be seen of it either in Balfour's figures of Agalena (Fig. 

 28 A and £) or in the figures of Locy, who examined another species of the same 

 genus. In other figures by the latter author, however, the presence of this 

 segment in the same species can be gathered with some certainty (Fig. 30 A). 

 By other authors, the first segment which is provided with limbs, i.e., the true 

 second segment, has been considered as the first. 



* Two recent investigators of the ontogeny of the Araneae, Jaworowski 

 (No. 5) and Kishinouye (No. 62), also state that in front of the segment which 

 carries the first large pair of abdominal limbs, and which was usually taken for 

 the first, another segment lies. These authors, however, did not find limbs on 

 this segment. That such limbs may be present is shown by the above descrip- 

 tion and figure. [6/. Brauer on Scorpiones, No. II.] 



