298 SUMMARY OF CURRENT RESEARCHES RELATING TO 



5. Arachnlda. 



Segments of Pseudoscorpionidse.* — J. P. Stschelkanovtzeff has. 

 studied the metameric architecture of three species of Chernes. The 

 cephalothorax (cephalon, prosoma) consists of nine segments ; the seg- 

 ment with chelicerse is the third metamere, and corresponds to the 

 intercalary segments in insects, and to that of the second antennas in 

 Crustaceans ; the mouth-opening lies in front of this metamere ; re- 

 mains of the sternum are seen in all the appendage-bearing segments 

 of the cephalothorax except the first two. 



The abdomen consists of eleven segments ; the sternites of the first 

 two segments share in forming the genital operculum ; the genital 

 aperture lies between the second and third abdominal segments. The 

 stigmata lie between the first and second, and between the third and 

 fourth. It is not justifiable to give segmental value to the conical pro- 

 tuberance on which the anus is situated ; it has no trace of musculature 

 indicative of independence. The total number of segments is twenty. 



Development of Dolomedes fimbriatus.f — P. Pappenheim ha3 

 studied the development of this large spider with special reference to 

 the brain and eyes. The head-lobes of the embryo shoAV no hint of 

 antennae ; there is no external segmentation of the head, but the head- 

 lobes include a pair of pro-cheliceral ccelomic cavities, suggestive of a 

 pro-cheliceral segment independent of the acron. The primordium of 

 the principal eyes is independent of the formation of the brain. The 

 brain begins with the invagination of lateral vesicles, resulting in two 

 semicircular pits. Two independent rostral folds form the principal 

 eyes, which lie further back in the adult. The accessory eyes which 

 appear in the region of the two lateral vesicles do not change their 

 place much. 



Pappenheim finds in the embryonic cephalothorax eight ganglionic 

 primordia : — apical groove primordia, lateral vesicle primordia, cheli- 

 ceral ganglia, pedipalp ganglia, and four other pairs corresponding to 

 the legs. The embryonic abdomen shows a composition out of eight 

 segments and a telson, but the nature of the abdominal nerve-cord 

 indicates a larger number (perhaps ten) abdominal metameres. 



New Hydrachnida and Ixodidas from South America.! — C. Ribaga 

 describes the genus ArrenureJla, various species of Arremirus, Eylais, 

 Hydrachna, and other new forms collected by F. Silvestri in South 

 America. 



Sheep Scab.§ — This is the subject of a recent leaflet from the Board 

 of Agriculture. The well-known disease is due to a mite, Dermatodectes 

 ovis or Psoroptes communis, resembling the mange-mite of dogs and 

 other animals. After a sheep-scab mite has been transferred directly or 

 indirectly from a diseased to a healthy sheep, the female lays its eggs 

 and dies. Under favourable circumstances the eggs are hatched in 

 about seven days, and the young female parasites, after undergoing the 



* Zool. Anzeig., xxvi. (1903) pp. 318-34 (8 figs.), 

 t Zeitschr. f. wise. Zool., Ixxiv. (1903) pp. 109-54 (2 pis.). 

 X Ann. Scuola Sup. Agric. Portici, v. (1903) pp. 1-28 (2 pis.). 

 § Leaflet No. 61 Board of Agriculture, 1903, pp. 6 (3 figs.). 



