1<! SUMMARY OF CURRENT RESEARCHES RELATING TO 



Spermatogenesis.* — Horr 0. S. Jensen studied the ontogeny of 

 Bpermatozoa in the rat, horse, sheep, and to some extent in man. His 

 research bears especially on the much debated point of the structure of 

 the tail, but some observations on the head-portion were also made. 

 The fibrillar composition of the axial filament, the apposition and not 

 twisting of the thread-like halves, the lumen passing up the entire axial 

 filament, the spiral thread round the axis-filament in the connecting 

 portion, are all minutely described and figured, but hardly call for 

 detailed summary. 



Two Young Human Embryos. | — Prof. J. Janosik has studied a 

 young normal and satisfactorily preserved human embryo. A second 

 less favourable specimen also came into his hands. The first was 

 probably the youngest human embryo as yet satisfactorily described. 

 It measured 3 mm. in length, the ovum itself 8 mm. ; the whole surface 

 was covered with villi 1 mm. in length. The relations of the skin, 

 body-wall, skeleton, nervous system, sense organs, alimentary tract, 

 urinowenital organs, heart and vascular system, are described in detail. 

 The embryo described corresponds to the embryo of M. His, which was 

 probably slightly younger, but less well preserved. The relations to 

 other young embryos are also noted. 



Experimental Embryology.^— Prof. L. Gerlach gives an interesting 

 account of a new method applicable to research in the comparatively 

 new field known as experimental embryology. 



There can be no doubt that a young form is more in the grasp of 

 environmental influences, and is more plastic towards them than an 

 adult can well be; an influence borne in persistently on a series of 

 generations during embryonic life must be of the most potent character. 

 That experimental embryology has not been earlier attacked has been 

 due on the one hand to the necessity for preliminary study of the normal 

 development, and on the other hand to the absence of a proper method. 

 To attack such a problem as that of testing mutability during embryonic 

 life, it is necessary that accessible embryos be obtained, that some know- 

 ledge be forthcoming as to the influence and application of definite, not 

 mortal external agents, and that it be possible to rear the subjects of 

 experiment. As regards accessibility, the ova of birds, amphibia, and 

 fishes are among Vertebrata the forms best adapted for experiment. The 

 external influences, the operation of which may be studied, are manifold, 

 from pressure to electric currents. Under increased pressure, Eauber 

 produced short compressed forms. With over-abundant oxygen, the 

 gills of tadpoles remained rudimentary. The influence of gravity on 

 segmentation has been abundantly studied. Eoux has investigated the 

 results of pressure and mechanical injuries. 



In spite of these and other important researches, there are many 

 obvious desiderata. It is necessary to have a more exact method of ex- 

 periment, the varying plasticity of the embryos must be appreciated, a 

 graduated series of influences must be established, and successive 

 generations must be reared. Experiments on the mutability of embryos 

 are still relatively premature, but birds afford the most convenient 

 subjects for experiment as to the operation of external influences and 



* Arch. f. Mikr. Anat., xxx. (1887) pp. 379-425 (3 pis.). 



t Ibid., pp. 559-95 (2 pis.). 



X Biol. Centralbl., vii. (1887) pp. 588-605. Anatom. Anzeig., 1887, pp. 18-9. 



