92 



ARACHNIDA. 



(Schimkewitsch), so that it is impossible to trace them back, as Balfour 

 attempted to do, to the partition walls of the somites. 



A structure resembling the fat-body of the Insecta which is present in 

 the body-cavity (Ray Lankester's lacunar blood-tissue) is, according to 

 Schimkewitsch, formed, like some of the blood-corpuscles, out of the yolk- 

 cells which immigrate into the body-cavity, and these cells also are said to 

 become arranged into a " peritoneal " layer, which envelops the internal organs. 

 In both cases we should, after what has already been said, feel disposed to 

 derive these structures from the mesoderm, i.e., from the primitive segments, 

 although such a derivation would have to be established by further researches. 

 Where a peritoneum is present, it would be of interest to learn its relation to 

 the primitive coelomic epithelium. 



rrv. 



Fig. 48. — Portions of transverse se.ctions of Pholcits phalangiddes (A) and Lycosa saccata (B 

 and C), through different regions of the abdomens of embryos (after Schimkewitsch). 

 bl, blood -corpuscles or detached mesoderm-cells ; e, ectodermal covering of the body; 

 g (and gi?), portions of the genital glands descending to the ventral side ; hi, median portion 

 of the rudiment of the ventral cord; ran, muscles; n, rudiment of the ventral cord; 

 so, somatic, sp, splanchnic layer of the mesoderm. 



H. The Coxal Glands. 



The coxal glands, which we shall describe as they are found in 

 the already hatched Araneid, show great resemblance to those of 

 Scorpio, and no doubt arise in the same way as in that animal. 

 An actual efferent duct has for the most part only been proved to 

 exist in young Araneids, where it opens at the base of the fifth 

 pair of appendages (Bertkau, No. 51). In the young of Atypus, 

 Bertkau found, on the anterior pairs of limbs, i.e., third and fourth 

 pairs of appendages, slits corresponding in appearance and position 

 to the apertures of the coxal glands on the fifth pair, and this led 

 him to conclude that there were originally several pairs of these 

 glands. 



