MR. H. M. BERNARD ON THE CHERNETIDiE. 423 



This striking difference in position shown by the vestigial 

 stigmata is rather remarkable, occurring within a well demarcated 

 group such as the Chernetida?. I would, however, point out that 

 the difference in the number of the abdominal segments claimed 

 for different genera is almost equally surprising. The group is 

 an extremely difficult one to classify ; and I am afraid that these 

 vestigial stigmata, visible only on carefully macerated specimens, 

 will not make the task easier, although it is obvious that they 

 are of prime importance for establishing a natural classification 

 of the group. 



These nine pairs of stigmata on the abdomen, rudimentary and 

 functional, make it almost certain that the primitive Arachnid 

 had tracheal invaginations on every segment. In the cephalo- 

 thoracic segments these tracheae have, as a rule, disappeared, 

 owing to the compression of the six segments which form this 

 region. We have cephalothoracic tracheae, however, in Galeodes, 

 in which the cephalothorax is jointed, and in certain Acarines 

 which have failed to develop the abdominal segments. Purther, 

 only a certain number of the abdominal tracheae have persisted ; 

 the anterior pairs have become, as a rule, specialized, while 

 the posterior pairs have disappeared. 



In addition to these stigmata, functional and vestigial, the 

 remarkable " ram's-horn " organs, described by Menge and again 

 by Croneberg, deserve special attention. It is claimed that 

 these organs are present in the males of all species and genera. 

 I succeeded in finding them only in one specimen, presumably 

 the only male ; its actual sex cannot now be determined, as the 

 genital glands have suffered from the attacks of the infesting 

 bacteria above referred to. In this single case, however, these 

 organs present features hitherto unnoticed, which go far to 

 establish Croneberg's belief that they must be homologous with 

 tracheae. 



They are large chitinous tubes, the walls of which are much 

 folded transversely, so that they are capable of considerable 

 extension. I doubt, however, whether this is the object of the 

 folding : it is rather for the sake of flexibility. They open 

 laterally under the genital operculum, which thus protects their 

 orifices. Menge says they are often conical, sometimes ram's- 

 horn-like ; they have this latter form in my specimen. Prom 

 their apertures they rise dorsally, then bend forward, dipping 

 down ventrally in a curve, the whole figure described being 



