377 



SUMMARY OF CUREENT EESEARCHES 



RELATING TO 



ZOOLOGY AND BOTANY 



(PEINCIPALLY INVERTEBRATA AND CRYPTOGAMIA), 



MICEOSCOPY, Etc.* 



ZOOLOCxY. 



VERTEBRATA. 



a, Embi-yoloery.t 



Experimental Embryology.^ — The late J. W. Jenkinson delivered 

 three lectures introductory to Experimental Embryology, whicli have 

 now been published. The first discusses growth, the structure of the 

 germ-cells, and fertilization. " When the germ -cells meet and unite in 

 the act of fertilization the full number of chromosomes {2n) is restored, 

 but that is not the only nor even the chief event involved in the 

 process. In fertilization four distinct events occur, and sometimes a 

 fifth. The first of these is the extrusion by the ovum of a fluid, the 

 perivitelline fluid ; the second is the entrance of the spermatozoon ; the 

 third is the appearance of the definitive centrosome and its division into 

 two to form the cleavage apparatus of asters and spindle ; the fourth is 

 the union of the male and female pronuclei. To these must be added, 

 in some cases at least, a fifth, the alteration of the structure and 

 symmetry of the Qgg.'''' 



The second lecture discusses four problems. The first of these is to 

 discover why the Qgg^ divides at all. The second is to find out why, 

 when it does divide, it exhibits its own particular pattern of cleavage. 

 The third inquu'es into the causes which bring segmentation to an end. 

 The fourth question asks whether cleavage is or is not in itself a process 

 of differentiation, the answer being in the negative, for it is held that 



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

 do not hold themselves responsible for the 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 pub- 

 lished, and to describe and illustrate Instruments, Apparatus, etc., 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, Reproduction, and 

 allied subjects. 



X Three Lectures on Experimental Embryology (Oxford, 1917) xvi and 130 pp. 

 (20 figs). 



Aug. ].5th, 1917 2 c 



