SUMMARY OF CURRENT RESEARCHES. 345 



which correspond bo the prophase of the heterotypical divisions occurring 



in plants and animals. 



The stage of synapsis is the mosl prolonged and of most importance. 

 The chromatin filaments undergo a pseudo-reduction during this stage, 

 and they undergo apparent Longitudinal division in the stage following 



the formation of the thick spireme. The nucleolus persists during all 

 the stages of transition of the nucleus, although its staining capacity 

 may vary. 



No evidence was found in the medullary curds of the presence of 

 cells that might lead to the formation of primary oocytes. The glandular 

 structures in the hilum are the remains of the Wolffian and rete tubules. 



Development of the Extremities in Birds.*— F. Sieglbauer pub- 

 lishes an account of his researches on the development of the skeleton 

 of the extremities in birds, showing especially the parallelism in the 

 early stages of the development of the widely different wing and foot, 

 and the relation of this to phylogenetic evolution. The development of 

 the wing and foot of the penguin, Pygoscelys papua, and of the duck, 

 Anas boschas, is described in detail, special emphasis being laid on the 

 phenomenon of heterochrony, which the author regards as of great 

 importance in the developmental history. The general results of the 

 paper may be stated as follows : — The skeleton of the foot of Pygoscelys 

 arises in the same way as that of the duck's foot. In the fifth toe of 

 the duck the lizard-character persists: while in the penguin, as in the 

 domestic fowl, onlv a blunt knob can be recognized in the later stages. 

 The first tibial toe, on the other hand, is much more highly developed in 

 the penguin than in the duck. The development of the skeleton of the 

 bird's wing and foot shows, in addition to the heterochronous characteristic 

 of the development of extremities in general, many points of agreement 

 with that of reptilian extremities. Since in the bird "'hand" the first 

 finger, as in Seps tridactyla, no longer attains to development, and the 

 second, fourth, and especially the fifth, remain rudimentary, the third 

 becomes the wing-bearing digit, and may be regarded as analogous to 

 the axis of the steering fin. The whole function of the wing-skeleton is 

 to form an articulated yet firm basis for the quills, and therefore the 

 bird hand is rudimentary and very unlike that of its ancestors. The 

 skeleton of the foot has changed much less in the course of phylogeny, 

 although the reptilian character has become blurred by the degeneration 

 of the first toe, by the complete disappearance of the fifth toe in the 

 ontogeny, and, above all, by the lengthening of the bones of the lower 

 leg and the metatarsals, and the fusion of the latter with the distal 

 tarsals. It is, above all, this lengthening of the leg-bones, and the 

 consequent raising of the body from the ground, that distinguishes the 

 birds from the creeping reptiles. This character is of advantage not 

 only in running but in taking flight from a flat surface. 



Development of the Limbs in Grebes.f— The late F. T. Rosenberg 

 made a study of the development of the limbs and bill in grebes. The 

 material used was chiefly the eggs of the black-necked grebe, the only 



* Zeitschr. wiss. Zool., xcvii. (l'Jll) pp. 262-311 (2 pis. and 16 figs.). 

 t Tom. cit.. pp. 119-217 (1 pi. and 13 figs.). 



