1894- NOTES UPON THE ORGANS OF ARACHNIDS. 363 



palaeontology which strongly support the generally-received view that 

 lung-books are the more primitive. A recent investigation (6) by 

 Mr. O. L. Simmons into the development of the breathing organs of 

 spiders supplies valuable embryological evidence upon the same side. 

 This observer finds that in species of Thevidion and Agelena the lung- 

 plates arise upon the hinder surface of abdominal limbs in exact 

 correspondence with the origin of the gill-leaves of Limulus, and 

 that the appendage simply sinks into the abdomen without inversion 

 or other compUcation, exactly in the way lately suggested by Dr. 

 Kingsley, and figured in Natural Science (vol. iii., p. 442). In 

 tracing the development of the tracheae (which in the higher spiders 

 replace the hinder pair of lung-books), Mr. Simmons finds a stage 

 showing folds indicative of the lung-plates, which vanish later. We 

 have here, then, another link in the strong chain of evidence that 

 among arachnids lung-books preceded tracheal tubes, and that they 

 represent the gill-bearing appendages of aquatic ancestors. 



Two interesting cases of virgin reproduction among arachnids have 

 recently been noted. Hitherto, the occurrence of parthenogenesis has 

 hardly been known in the class, though instances among the other 

 two great arthropod classes — the crustaceans and insects — are suffi- 

 ciently familiar. Now, however, M. Trouessart has (7) brought to 

 light a case among the mites, and Herr Damin (8) one among spiders. 

 The former observer has studied a species of sarcoptid [Syringobia) 

 which infests the wing-feathers of the Redshank {Totanus calidris). 

 While the bird is on its migration between its northern summer 

 breeding haunts and its southern winter resorts, two kinds of 

 colonies of the mite are found within the quills. The normal colony 

 consists of males and females in their adult and preparatory stages. 

 In the parthenogenetic colony are found specially modified females, 

 incapable of impregnation but producing fertile eggs ; very rarely, a few 

 abortive males are present. During the bird's sojourn in the south the 

 mites live freely upon the barbs of the feathers ; when the time for 

 migration draws near, three or four in the nymph stage of develop- 

 ment enter the quill. According to M. Trouessart, if both sexes be 

 represented among these, a normal colony will result, but if all be 

 females they will become capable of virgin reproduction — a truly 

 remarkable adaptation to their confined mode of life during the 

 period of migration. 



The parthenogenetic spider observed by Herr Damin was a 

 female of Filistata testacea, a species common in the south of Europe. 

 Taken while still immature, this spider underwent two moults, and 

 then, never having been in company with a male, spun a cocoon and 

 laid eggs, which in due time hatched, producing healthy young. Some 

 time after this, strangely enough, another casting of the skin took 

 place. In connection with his observation, Herr Damin notices 

 that while females of Filistata are very common, the male is ex- 

 ceedingly scarce. 



