ZOOLOGY AND BOTANY, MICKOSCOPY, ETC. 25 



Skeletal Changes in Flat-Fishes in the Course of Development.*— 

 O. Thilo discusses these partly from the standpoint of one accustomed 

 to deal with mechanical problems, and partly from the standpoint of an 

 ophthalmologist. The result is a very interesting essay, to "which we 

 cannot do justice in this brief summary. Why do flat-fishes swim on 

 one side ? This is the natural result of a change in body-form, and has 

 associated with it a number of remarkable changes — extension of median 

 fins to the head, forward displacement of anus, degeneracy of paired 

 fins, deformation of the urohyal, degeneration of swim-bladder, and 

 migration of one eye. 



What forces influence the migration of one eye ? There are traction- 

 forces due to the eye-muscles, and Stiitzkrafte due to ossifications in 

 the vicinity of the eye, and to the influence of the migrating eye on its 

 still cartilaginous skeletal surroundings. 



Development of Vertebrate Lung.f — Fanny Moser has studied this 

 in Amphibians, Reptiles, Birds, and Mammals. In every case the 

 principle is the same : — {a) there is a general increase in size by pro- 

 liferation in the tissues ; and (b) there is a special increase of the 

 endodermic epithelium which, as the intrapulmonary bronchus, grows 

 into the solid connective tissue around it. 



If the connective tissue is loose and sparse, the increase of the in- 

 ternal epithelium is associated with a direct and diffuse general out- 

 pushing of the wall, and with an enlargement of the intrapulmonary 

 bronchus (as in Amphibia). If the connective tissue is thick and 

 resistant, the epithelial proliferation is localised at particular areas, and 

 results in bud-like outgrowths insinuated into the connective tissue. 



Certain parts of the wall that are very resistant to expansion project 

 inwards as if they were septa. The number of buds of the second order 

 decreases as we ascend the Vertebrate series, and the mass of connective 

 tissue increases. Thus the result tends to be a system of long, narrow 

 canals penetrating a thick connective-tissue-sac (Birds and Mammals). 



The branching system of the canals within the lung is always mono- 

 podial. In every lung there is demonstrable — on to the distal end — 

 a principal canal, the intrapulmonary bronchus (mesobronchus, Stamm- 

 bronchus, bronche souche, &c), the direct continuation of the extra- 

 pulmonary bronchus. 



Solution of the Eel Question. :{: — Carl H. Eigenmann has come to 

 the following conclusions : — (1) Both male and female eels migrate to 

 the ocean during October to January. (2) The female migrants of 

 this period probably deposit the eggs that are found on the surface 

 during the following August to January: (3) Female eels never mature 

 in shallow water ; according to Grassi, maturity occurs at a depth of 500 

 metres. (4) The eggs float, — according to Raffaele and Eigenmann at 

 the surface, according to Grassi at a great depth. (5) The larva differs 

 markedly from the Leptocephalus-sta,ge, and the latter from the adult. 

 (6) The young eel found entering the stream is the result of a meta- 



* Zool. Anzeig., xxv. (1902) pp. 305-20 (19 figs.). 



t Arch. Mikr. Auat., lx. (1902) pp. 5S7-668 (4 pis. and 3 figs.). 



X Trans. Amer. Micr. Soc, xxiii. (1902) pp. 1-18 (4 pis.). 



