329 



SUMMARY OF CURRENT RESEARCHES 



RELATING TO 



ZOOLOGY AND BOTANY 



(principally invertebrata and cryptogamia), 



MICKOSCOPY, Etc.* 



ZOOLOGY. 



VERTEBBATA. 



a. Embryolog'y, Evolution, Heredity, Reproduction, 

 and Allied Subjects. 



Maturation of Human Ovum. — Arthur Thomson (Journ. Anat., 

 1919, 53, 172-208, 3 pL, 18 figs.). The human ovum is not spherical, 

 but ovoid. The diameter, including the zona pellucida, is about 

 0-11 mm. The zona pellucida has its thickness reduced by the per- 

 meation of fluid through it, so that its elements separate into strands or 

 small groups of fibrils. Lining its inner surface there seems to be 

 a distinct vitelline membrane. The zona pellucida sometimes shows 

 a faint appearance of concentric lamination. It is suggested that the 

 radial striation only occurs in the later stages of maturation. There 

 seems to be a perivitelline space, largest at the time of the extrusion of 

 the polar bodies which eventually come to lie within it. There is 

 evidence of a centrosome which divides into two. There are vacuoles, 

 often with a granule within, and isolated granules in the cytoplasm. 

 The nucleus ranges in size from • 020 x 0-017 to 0' 030 x 0- 024 mm.; 

 it may show a membrane or none ; its contents include chromatin 

 granules, isolated, paired, massed in groups, or arranged in threads. A 

 clearly defined nucleolus may be seen. The karyoplasm is paler and more 

 finely granular than the cytoplasm. Both polar bodies seem to be 

 expelled before the oocyte has left the Graafian follicle. In other words, 

 the maturation of the oocyte with its female pronucleus is complete 

 before it has been subiected to the influence of the spermatozoon. 



J. A. T. 



Formation of Single-ovum Twins. — George L. Streeter {Bull. 

 Johns Hopkins Hospital, 1919, 30, 235-8, 4 figs.). In a very early twin 



* The Society does not hold itself responsible for the views of the authors 

 of the papers abstracted. 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, etc., which are either new or have not been previously 

 described in this country. 



