ZOOLOGY AND BOTANY. MICKOSCOPY, ETC. 207 



single millimetre in the scale of length is represented. Particular 

 attention is paid to the development of the teeth and of the anal and 

 caudal fins. The changing proportions of the tail during development 

 are discussed. Schmidt also gives an account of the differences be- 

 tween the fresh- water eels and other North Atlantic Murasnoids in their 

 early (" preleptocephaline ") larval stages, and defines four species. 



Eggs of Gaflf-topsail.* — E. W. Gudger gives a very interesting 

 account of the way in which the male of Felichthys fells — a sub- 

 tropical marine catfish — takes care of the eggs, incubating them in 

 its mouth. From two to fifty-five eggs were found in the mouths 

 examined, most of them 18-20 mm. in diameter, with very fluid yolk. 

 They develop in the mouth till the young are hatched, when they 

 are 85-100 mm. long. The enormous mouth is dilated when the 

 eggs are in it, the gill-covers being widened outwardly and the hyoid 

 distended downward. In the male that had fifty-five eggs in the 

 mouth, the volume of the mouth was about 580 c.cm. The length 

 of the period of incubation cannot be stated definitely, since it was 

 not found possible, in spite of many attempts, to carry the develop- 

 ment of the eggs on to the stage of hatching. It probably lasts about 

 seventy days. During all this time the paternal nurse does not seem 

 to feed. If the large eggs were spawned on sandy or shelly bottom? 

 they would be destroyed by crabs or by fishes. If they were laid on a 

 muddy bottom their considerable weight would cause them to sink into 

 the mud, where they would be smothered. 



b. Histolog-y. 



Comparative Study of Thymus.f— J. Salkind has made a compara- 

 parative histological study of the thymus in mammals, birds, reptiles, 

 amphibians, fishes, and lampreys. He inquires into the physiology and 

 chemistry of the organ from the microscopical side. Starting from the 

 parapharyngeal grooves in lancelets, the author regards the thymus as 

 primarily a local differentiation of the enteric endoderm. In larval 

 lampreys it has become an annex of the gill-pockets. In Selachians it 

 keeps its correspondence with the gill-clefts, but is separated off as a 

 lymphoid annex of the gills. In Teleosteans it loses its branchio- 

 merism. In tadpoles a limited number of patches of epibranchial 

 epithelium form the organ ; in adult Batrachians it gets away from the 

 alimentary tract and approaches the surface. In Sauropsida the super- 

 ficial movement is more marked, the organ becomes more lateral and 

 more distinct from the gut. But it retains its distinctive character as 

 a lymphodization of an endodermic primordium as the result of con- 

 nective proliferation. In mammals the lateral position is changed to a 

 ventral one, which is acquired in very early embryonic stages. Through- 

 out the series the thymus, as regards the lymphatic system, is a simple 



* Zoologica, ii. (1916), p. 125-58 (12 figs.). 



t Arch. Zool. Exp6r., Iv. (1915) pp. 81-322 (3 pis. and 54 figs.). 



