338 SCIEXCE PROGRESS. 



web of the Spiders^ for instance comes partly from glands 

 which are serial with the cement glands of the Book- 

 scorpions. These again are apparently homologous with the 

 gland supplying the coarse silk for the cocoon of Phrynus 

 and the glutinous matter sticking together the eggs of 

 Thelyphonus. Again, the web-spinning glands of the Book- 

 scorpions open at the tips of the jaws close to where, in 

 the Spiders, the poison glands open ; while the glands 

 of the spinning Mite (Tetranychus) open in the cor- 

 responding place on the second limbs, and the poison 

 glands of the Scorpion open at the tip of the sting which I 

 regard as a pair of fused limbs (see above). Lastly, the 

 poison glands of Scorpio are probably homologous with a 

 pair of large glands in Thelyphonus said to emit an 

 offensive and volatile fluid, only here the limbs have 

 degenerated and the glands open one on each side of the 

 anus. 



Of the above-mentioned glands the Galeodidae possess 

 only one pair, and that of a very simple character. They 

 open just within the genital aperture and probably yield a 

 sticky secretion for the eggs ; there are no poison glands, 

 no spinning glands, no "stink" glands. This is important, 

 for it indicates that none of these glands in their specia- 

 lised forms were present in the ancestral Arachnid. Indeed, 

 this is obvious from the fact that they do not appear in 

 exactly the same place and character in any two existing 

 Arachnids, whereas had they developed in the ancestral 

 form, we should have found more uniformity in their 

 distribution and character in its descendants. But the 

 Galeodidse, if they have no glands, are as we have noticed 

 above, extremely rich in bristles and hairs, and this same 

 character we may safely predicate of the ancestral form. 

 We shall probably then not be far wrong if we trace 

 back all these o^lands to the small cuticular sacs out of 



o 



^ It is worth noting that the marvellous web-spinning of the Spiders, 

 and secondarily also the peculiar form of their abdomens are, in all proba- 

 bility, due to the early fixing of their spinning-glands far back on the abdo- 

 men. This position, the movement being from the waist, gave the threads 

 a longer throw. 



