" Eminent ia dorsuaUs" on fourth Tarxux in the Males 65 



operculum genitale are grounded on the difference in shape between penis and ovipositor. 

 From the description of these organs which we have given in the preceding chapter, it 

 will have been gathered that, particularly in Laniatores, Ischyropsalidoidte, Nemastomatoidaj, 

 and Troguloida;, penis is anteriorly much more slender than ovipositor. Accordingly the 

 genital orifice is narrower in the male than in the female, and, as a consequence of this, 

 operculum genitale is narrower and therefore proportionally — in some cases even absolutely — 

 longer in the male than in the female. We may mention, for instance, that by this means 

 the sexes are more or less easily distinguished in Troguloidse, which has not hitherto been 

 possible ; in the male of Dicranolasma operculum genitale is almost exactly as lono- as 

 it is broad, and in its posterior half the lateral borders converge but slightly towards 

 the anterior extremity; but in the female operculum genitale is strikingly broader than it is 

 long, and its lateral margins converge considerably fi'om the base forwards. In the sub-family 

 Trogulini E. S. the difference is mcjre difHcult to appreciate ; in the male Trugidus sinuosus W. S. 

 operculum genitale is four to five times broader than it is long, an<l the lateral borders 

 are less curved and form a more distinct angle with the anterior border than in the 

 operculum genitale of the female, which besides is about six times broader than it is long. 



In Cyphophthalmi the case is different. In this group zoologists have hitherto not 

 been able to distinguish the sexes by external characters. ThLs, howevei-, was only owing to 

 the fact that these animals have hitherto been but imperfectly examined, .since it is precisely 

 for them that we find ourselves able to give at least two sexual characters, of which moreover 

 one is highly distinctive, while of both we may venture to say that they hold good for all 

 members of this sub-order, and not only for those which we have examined. The leadino- 

 character is taken from the shape of the fourth tarsus. In the females this increases in 

 thickne.ss, uniformly but not considerably, from the base to its distal end. In the males, 

 on the contrary, the fourth tarsus carries on its dorsal side, more or less near the base, 

 what we in our descriptive text call " eminentia dorsualis." This may be described as con- 

 sisting of a basal part and a less stout distal portion, which is flattened and pointed. 

 These parts are of somewhat different shape in different species, and will therefore be 

 treated of in our descriptions of species. That part of the joint where eminentia dorsualis 

 appears is more or less enlarged. This is the case only to a small degree in Stylocellus, 

 the one genus vs-hich is endowed with eyes; it is much more, and conspicuously, enlarged 

 in all the other genera, in none probably more than in Purcellia and in Siro rubetis ; in 

 this latter .species the joint (PI. IV., fig. 2 d) is enlarged on the dorsal side in nearly the 

 whole of its length. This enlargement of the fourth tarsus and its " eminentia dorsualis " 

 in the males are only an external evidence of the much more essential fact that this 

 enlarged part of the joint contains a gland which is absent from the females. As shown in 

 PI. v., fig. 2 n, the common excretory duct of this gland widens towards the opening which, 

 at any rate in Purcellia, Parasiro, and Siro duricorius'^ , has a situation rather distant from 

 the distal extremity of eminentia dorsualis. On account of the conformation of the excretory 



^ We discovered this gland only when we had already one specimen before us, the only one known to exist in any 



returned the specimens of Pettalus, which we had borrowed, collection, but without tlie application of a rather strong 



and when we had already dissected the specimen of Stylo- magnifying power it is impossible to decide where the opening 



cellus which we could spare for anatomical research ; and of the gland is situated. On this point therefore we are 



the chitine of Stylocellus is so thick that it is impossible unable to give any information as regards S((//oeeHHS,Pe«afes 



without dissection to discern the inner organs even in a part and Siro rubens. 

 as slender as the tarsus. Of Siro rubens we have had only 



s. 9 



