246 S- H. Buxton, 



but the cells are generally much worn down and the nuclei lie 

 almost bare of cytoplasm on the free border of the striation. 



Photograph 23 shows the passage of the saccule into the exter- 

 nal tubule and photograph 24 the saccule and internal tubule. Dia- 

 gram A explains of itself how the internal tubule at this point 

 appears to be double. The photographs 21 to 24 are taken from 

 sections cut transversely approximately at the points indicated by 

 the broken vertical lines in the diagram. 



Group 2. The hunting Lycosids, Thorn isids, Attids, 



Drassids, Zodariids, Selenopids, Ctenids, and the 



imperfect web spinners, Agelenids and Dictynids. 



The labyrinth in the members of this group of spiders shows 

 very close resemblances, and one description will serve for all. 



The walls of the external tubule leading posteriorly from the 

 saccule, have become very thin and are lined with a flattened epithe- 

 lium, the nuclei of which are not prominent so that the tubule 

 resembles the saccule, and until the tubule is closely followed up 

 from section to section it is often difficult or even impossible to 

 determine which is the saccule and which the external tubule. 



The external tubule runs, as in the Dysderid group, posteriorly 

 to the sixtli appendage where it turns forwards again. At the turn, 

 or a little before the turn (photo 25, 25 a) the lining epithelium 

 changes its nature and becomes cubical and larger, remaining how- 

 ever relatively fine and delicate, and showing no evidence, or 

 mere traces, of the striated base, which is such a marked feature 

 in the typical labyrinth. The internal tubule is usually greatly 

 dilated and shows dips towards the surface between the fourth and 

 fifth, and the fifth and sixth appendages. 



It has also dorsal extensions opposite the dips and also one 

 opposite the exit. It would seem to serve the purpose of an ex- 

 tensive bladder rather than of an excretory gland (photo 26, 27) 

 and probably the saccule alone has excretory functions. In some 

 members of this group, e. g. the Zodariids (photo 28) the external 

 tubule seems to have become actually fused with the saccule. 

 The process of fusion appears to be due to glomeruli pushing 

 in the thin wall of the tubule, so that its lumen becomes 

 irregular and broken up, glomeruli hanging into it, as into the 

 saccule itself. 



