50 



and if we examine it from the thus estal)lished opening, it is (juite bewildering to 

 look into this confusion of hairs, almost filling the hollow. The ridges which 

 adorn the walls of the sac attain a very remarkable development; their principal 

 direction is a transverse one, less visible terminally, where they arc densely placed 

 on all surfaces with longitudinal communication between them, but very distinctly 

 so in the middle, where the principal ridges are continued into eacli other posteriorly 

 giving the whole a ringed appearance; near the base they are only partly extended 

 to the posterior margins of the dorsal and ventral surfaces; the posterior surface 

 has no ridges at all basally. The basal or interior surface is especially behind the 

 funnel provided with short, densely placed ridges (fig. 6 c, r'). The ridges bear at 

 least distally not only subconical tubercles, but also laminae, extending into the 

 lumen of the sac. The skin of the sac is minutely dotted all over. 



8. Ch. Socotrensis With (21. pp. 135—136, pi. VII, figs. 4 b-f ). With regard to 

 the structure of the coxal sac of this species I refer to the description ; which is 

 distinguished from all those described here by being so extremelj' small, only 

 occupying a tenth or a twentieth of the lumen of the coxa. But it is in all other 

 particulars highly developed, providing similarity to that of Ch. Mortensenii n. sp. 

 by the well separated and big basal portion with a higly develo[)ed "funnel". 



Concluding remarks. — What is the function of this remarkable organ? 

 To answer this question will really be difficult. No muscles seem to be fastened 

 to its wall and no glands seem to discharge there; the hairs are |)0ssibly connected 

 with nerves. The organ is a comparatively big sac with well chitinized walls only 

 communicating with the outside world through a diminutive opening at the base 

 of the coxa of the fourth pair of legs; for the animal to turn inside out by the 

 pressure of the blood or otherwise may be deemed impossible. This organ is only 

 found in the males of a very limited group of species and provides within this 

 group the most startling variations. It seems to me most probable to regard it as 

 a sense organ of some way related to the sexual life; it will probably be fairly 

 easy to prove, if this conjecture is right or wrong, by applying histological methods 

 on fresh material, which is unfortunately very difficult to obtain. Direct observa- 

 tion in nature gives of course also a chance, even if only small, of coming to an 

 understanding of these problems. Or should there be any relation between the 

 coxal sac and the ram's-horn-shaped organ? 



Other questions remain to be answered; how early in the life of the male 

 can this organ be traced; I have only examined il in fullgrown males and in a 

 single specimen of Ch. Mortensenii n. sp., which had apparently not yet passed its 

 final moult. To answer this question and eventually to give a description of its 

 embryologicai development will scarcely prove very difficult when material is avail- 

 able, and should show itself useful from a comparative point of view. To answer 

 the question definitively, whether of the already described forms of coxal sac pro- 

 vide the most ]n-imitive characters, the investigation of this organ in a number of 

 species, greater than that, which has been examined here, will surely be necessary; 



