TRANSACTIONS OF SECTION D. 657 



drawn away from the neural tube, and examination of series of sections brought 

 out the fact that the rudiments of the motor trunks already connected myotome 

 and central nervous system at this period of development — before they had begun 

 to recede from one another with the interposition of mesenchyme. Zepidosireii 

 thus affords a definite anatomical basis for the view that the nervous bridge 

 between nerve-centre and end-organ exists from the beginning, and that the growth 

 of the nerve is a drawing out of this bridge as the end-organ is pushed away by 

 the development of underlying mesenchyme. 



I have so far been able only in the case of the motor trunks to trace them 

 back to this stage ; in the case of some of the sensory nerves of the head I have 

 got back to the stage in which the nerve-trunk appears to be developing in its 

 sheath of protoplasm, and I have no doubt that in time research will show that 

 this stage is preceded by exactly the same stages as is the case with the motor 

 nerves. 



The motor trunk in the earliest stage which I have seen has the appearance of 

 a simple protoplasmic bridge. It is very thin, and there is no obvious appearance 

 of fibrillation. AVhat happens to it within the wall of the neural tube observation 

 does not show. In well-preserved specimens the wall of the neural tube shows 

 no structure except nuclei closely packed in granular protoplasm, in which cell- 

 boundaries can scarcely be distinguished. At its outer end the nerve-trunk splits 

 up and is continued into the substance of the muscle-cells. 



5. The DeveJojmient o/Xenopus (Dactylethra). £1/ E.J. Bles, B.Sc. 



6. Exi^eriments on the Axolotl : Adaptations to Life in an Alkaline Medium, 



By E. J. Bles, B.Hc. ' 



7. On the Insect Fauna of some Irish Caves. 

 By George H. Carpenter, B.Sc. 



Only a few of the numerous caves in the limestone districts of Ireland have 

 as yet been searched carefully for a living fauna, but these have already yielded 

 results of considerable interest. The present communication deals with the 

 Springtails (CoUnnbola) that have been discovered in the Mitchelstown Cave, 

 near Cahir, Co. Tipperary, and in the Dunmore Cave, near Kilkenny. 



An exploration of the former cave in 1857 by Hal iday and Wright resulted 

 in the discovery of many specimens of a white blind springtail that was doubtfully 

 identified with the Carniolan cave species, Lipura sHlicidii, Schiodte. This 

 insect is now known to be identical with the widespread L. incrmis, Tullberg, a 

 species that inhabits both caves and the upper world in many parts of Europe 

 and North America. All the species of this genus, whether in caves or above 

 ground, are destitute of eyes. 



All the Irish caves seem to be inhabited by Tomocerus tridentlferus, 

 Tullberg, and in this species pigment and eyes appear to be always" well 

 developed. 



Heteromurus margaritatus, Wankel (= Templetonia cavernicola, Car- 

 penter), a pale blind specips, inhabits both Mitchelstown and Dimmore caves. 

 This form is widespread in the Continental caves, and has not yet been discovered 

 above ground. But it is closely allied to H. nitidus (Templeton), that occurs in 

 mould. 



Pseudosinella cavernarum (Moniez) abounds in the Mitchelstown Cave. 

 This is a blind white species that was first discovered in a deep cavern in the 

 South of France. It has since been found in quarry-tunnels and in nnts' nests in 

 Scotland, and under stones on fields in Norway. Its congener, P. alba 

 (Packard)— hitherto unrecognised in the British Isles, occurs in Dunmore Cave 



1902. ua 



