ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 509 



cell-mass, which constitutes the rudiment of the notochord, taking no 

 part in the splitting. After the splitting has become marked, the 

 notochord becomes separated off from the lower germ-layer ; iu its 

 cranial region it is a derivative of the endoderin, and in its caudal region 

 of the upper wall of the neurenteric canal. 



Abdominal Ribs in Reptiles. * — L)r. A. Voeltzkow and Prof. L. 

 Doderlein discuss, the former the ontogenetic development of these 

 structures in crocodiles and Hatteria, and the latter their phylogenetic 

 significance. Voeltzkow finds that in Crocodilus the ribs arise in the 

 subcutaneous connective-tissue outside the ventral muscles at the same 

 time as the covering-bones of the head, and are bony from the first. 

 There is no direct relation between them and the ventral muscles. In 

 their relation to the muscles, the abdominal ribs of Hatteria and 

 Crocodilus appear to be completely homologous. Prof. Doderlein argues 

 that this result entirely confirms the conclusion, which has long been 

 probable on palteontological grounds, that the abdominal ribs (ventral 

 skeleton) are the remnants of a dermal skeleton, and are entirely homo- 

 logous with the membrane bones of the skull and shoulder-girdle. 



Development of the Permanent Kidney in Amniota.f — Dr. XL 

 Gerhardt has studied this much-discussed problem in embryos of white 

 mouse, pig, dog, and fowl. He comes to the following conclusions : — 



(1) In Amniota the permanent kidney is a new organ, which takes its 

 origin from the archinephric duct, but not from the primitive tubules. 



(2) The Malpighian bodies of the permanent kidney are spatially and 

 developnientally quite distinct from those of the primitive kidney ; they 

 arise through the invagination of the peripheral blind end of a renal 

 canaliculus by a vascular coil. (3) The peripheral portions of the 

 renal canaliculi arise by the continuous growth of the collecting tubes. 

 It was not demonstrable that the canals formed in the cortex enter 

 secondarily into connection with those of the medulla. (4) Permanent 

 kidney and primitive kidney are not homologous ; they do not develop 

 in the same way. 



Regeneration of Bone in Urodela. % — Dr. H. Wendelstadt has ex- 

 perimented with axolotls and newts. Bone and cartilage in Urodela 

 are regenerated only from bone and cartilage, and in the direction of 

 embryonic growth. In a much injured arm, regeneration in a centrifugal 

 direction may form a fresh set of bones, even when the old set, displaced 

 by the injury, is still present. The ulna does not regenerate the radius, 

 nor the radius the ulna ; in fact there never is regeneration of a 

 laterally adjacent separate piece of skeleton. In the centripetal direc- 

 tion, there may be mending (Ausbesserung), but no distinct replacement 

 was demonstrated. As to the amount of regeneration, it may be noted 

 that from the humerus there may be a regeneration of the fore-arm 

 and of the hand. 



Tympano-Eustachian Passage in the Toad.§— H. Fox has investi- 

 gated the development of the tympano-eustachian passage and associated 



* Abb. Senckenberg. Nat. Ges., xxvi. (1901) pp. 315-36 (3 pis. and 1 bg.). 



t Arcb. Mikr. Anat., lvii. (1901) pp. 822-42. 



X Tom, cit., pp. 799-822 (3 pis.). 



§ Pioc. Acad. Sci. Pbiladelpbia, 1901, pp. 223-60 (4 pis.). 



