so 



ARACHNIDA. 



an outer exopodite (Jaworowski). Spinning glands may develop on 

 both rays, and it is thus suggested that the primitive number of 

 spinning mammillae was eight. No existing Spiders are known in 

 which these eight mammillae are fully developed as functional organs ; 



iau 



Fig. 41.— Longitudinal sections through embryos of Tkcridium mamdatum, at different stages 

 (after Morin). a, anus; bl, blood-corpuscles; d, yolk; dz, yolk-cells; g, brain; h, heart; 

 hepatic lobes ; m, mouth ; md, rudiment of the enteron ; mu, muscles ; n, ventral ganglia ; 

 rb, rectal vesicle ; s, indication of external segmentation ; sp, splanchnic layer of the 

 mesoderm ; vd, stomodaeum. 



in Liphistius (Pocock), however, the full number are present, but 

 only the four external ones (exopodites) possess functional spinning 



glands 



In the Dipneumones, we find present six functional mam- 



