368 SUMMARY OF CURRENT RESEARCHES RELATING TO 



SUMMAEY 



OF CURRENT RESEARCHES RELATING TO 



ZOOLOGY AND BOTANY 



(principally Invertehrata and Cryptogamia), 



MICROSCOPY, &c., 



INaUDING ORIGINAL COMMUNICATIONS FROM FELLOWS AND OTHERS* 



ZOOLOGY. 



A. VERTEBRATA :— Embryology, Histology, and General. 



a. Embryolog-y-t 



Mechanism of Development.^ — Dr- W. Eoux continues his researches 

 on the mechanics of embryonic development. The present contribution, 

 which is the fourth of the series, is specially devoted to the investigation of 

 the manner in which the disposition of the median plane of the frog embryo 

 is determined by the direction of conjugation of male and female nucleus. 



(a) In normal conditions, when the ovum is unconstrained and when it 

 has not been altered by too long delayed spawning. (1) The unfertilized 

 ovum has only one main direction of the future median plane of the embryo 

 determined — by the bipolar arrangement of the yolk-material. The axis 

 from black to white pole represents the dorso-ventral direction of the real, 

 the' cephalo-caudal direction of the final embryo. (2) Of the meridian 

 planes through this egg-axis, that in which the two nuclei conjugate be- 

 comes the median plane of the embryo. (3) But the direction of conjugation 

 is not fixed, but may be displaced by " localized fertilization " to any meri- 

 dian. (4) The fertilized side of the ovum becomes the ventro-caudal side of 

 the embryo, the other the dorso-cephalic. 



(5) The first division of the segmentation nucleus occurs in the direction 

 of conjugation. The separation of the two halves takes place at right 

 angles to the direction of division. (6) The coincidence of the direction 

 of conjugation and plane of division has this functional import, that only 

 in this case is the efi'ect of conjugation subject to no miscarriage by the 

 division. It expresses the simplest mechanism of the division of masses 

 united, but not completely mixed in conjugation. (7) The first yolk 

 division occurs in the meridional plane parallel to the direction of conjuga- 

 tion, and eventually coinciding with it. (8) The direction of conjugation 

 determines the direction of the first segmentation of the nucleus, that the 

 first yolk-division, and eventually the disposition of the embryo in the egg. 



* The Society are not intended to be denoted by the editorial " we," and they do not 

 hold themselves responsible for tlie views of the authors of the papers noted, nor for 

 any claim to novelty or otherwise made by them. The object of this part of the Journal 

 is to present a summary of the papers as actually published, and to describe and illustrate 

 Instruments, Apparatus, &c., which are either new or have not been previously described 

 in this country. 



t This section includes not only papers relating to Embryology properly so called, 

 but also those dealing with Evolution, Development, and Reproduction, and allied 

 fiubjects. 



X Arcli. f. ]\Iikr. Aiiat.. xxix. (188?) pp. ] 57-212 (I pi.). 



