'48 



ARACHNIDA. 



the posterior to the telson, with the as yet undifferentiated segments of the 

 post-abdomen, and the middle part giving rise to the other segments of the 

 body (p. 6). 



It is well to bear in mind how extremely difficult it is to orient the regions of 

 the body in these early stages of the Araneid embryo (cf. Figs. 23-25). This 

 difficulty throws some doubt upon the correctness of the identification of the 

 body-segments, given above on Salensky's authority, and consequently the 

 whole order of formation of the thoracic somites may be at fault. 



Fig. 25.— Embryos showing varying degrees of segmentation, but not yet provided with 

 limbs. A and B, Pholcus opllionoidcs ; C, Clubiona (after Claparede). A and B, lateral 

 aspects; C, ventral aspect, ch, cheliceral segment; c.pr, primitive cumulus ('?); eh, egg- 

 integument; h, posterior, Tel, cephalic lobes; ped, pedipalpal segment; I-IY, thoracic 

 segments ; 1, first abdominal segment ; si, caudal lobe ; r, anterior. 



The segments of the pedipalps and chelicerae are said by almost 

 all authors to appear later than the four thoracic segments. Just as 

 the posterior region of the embryo contains in itself a number of 

 segments, so also does the anterior lobe comprise, besides the cephalic 

 part, the segments of the chelicerae and the pedipalps. A regular 

 separation of segments from before backAvard, therefore, does not 

 take place. At the stage in which there are six segments interposed 

 between the cephalic and caudal lobes (Fig. 25 A and B) the four 

 posterior segments are much better developed and more distinctly 

 marked off than the two anterior segments. Balfour, Schimke- 



