,204 



SUMMAKY OF CURRENT RESEARCHES 



RELATING TO 



ZOOLOGY AND BOTANY 



(PEINCIPALLY INVEETEBRATA AND CEYPTOGAMIA), 



MICEOSCOPY, Etc.* 



ZOOLOGY. 



VERTEBRATA. 



o. Embryolog-y.t 



Experimental Embryology.l — E. W. MacBride calls attention to 

 the definite proof of organ-forming substances in the ovum which has 

 been furnished by the experiments of Crampton, "Wilson, Conklin, and 

 others. If the first polar lobe in the developing ovum of Dentalium is 

 cut off, the trochophore larva is devoid of the apical plate, the apical 

 tuft, the mesoderm, and the post-trochal region. If the second polar 

 lobe is cut off, the trochophore is devoid of mesoderm and post-trochal 

 region. The segregation of different substances in the Ascidian ovum 

 is the real cause of the differentiation of the germ-layers. Experiment 

 also shows that the condition of the formation of a normal frog embryo 

 is the proper spatial relationship between two organ-forming substances. 



Observation and experiment confirm the view that the organ-forming 

 substances emanate from the chromatin of the nucleus. The formation 

 of these substances appears to last for only a short period ; after that 

 the nuclei appear to be without formative influence on the cytoplasm. 

 But in animals like Polyzoa and Ascidians which bud, this budding 

 could be best explained as due to a renewed production of organ-forming 

 substances by the nuclei. These substances are often not distributed 

 to the formative tissues of the bud in the same manner as in the 

 embryo, hence the development of the bud often follows a different 

 course from that initiated by the embryo. 



* 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, Deveiopment, Reproduction, and 

 allied subjects. 



X Nature, xcviii. (1916) pp. 120-3. 



