290 



SUMMARY OF CURRENT RESEARCHES 



RELATING TO 



ZOOLOGY AND BOTANY 



(PKINCIPALLY INVERTEBRATA AND CRYPTOGAMIA), 



MICBOSCOPY, Etc.* 



ZOOLOGY. 



VERTEBRATA. 



a, Embryolog-y, Evolution, Development, Reproduction, 

 and Allied Subjects. 



Further Experiments on Sex of Frogs developed from Artificially 

 Activated Eggs. — Jacques Loeb {Proc. Nat. Acad. 8ci., 1018, 4, 

 60-62) has succeeded in rearing twenty leopard frogs produced by the 

 methods of artificial parthenogenesis from unfertilized eggs. Some 

 reached the age of ten to eighteen months, and nine were alive when the 

 paper was published (March 1918). Some have reached tiie size of the 

 full-grown normal adult male. Both sexes are represented ; seven of 

 the nine older whose gonads were examined were males, and two were 

 females. The males possess the diploid number (26) of chromosomes. 

 It is not known whether the female or the male is homozygous for sex 

 in the frog. J- A. T. 



Zona Pellucida in Turtle Eggs. — Alice Thing {Amer. Journ. 

 Anat., 1918, 23, 237-57, 12 figs.) finds that the epithelium surrounding 

 the ovarian egg of various turtles is represented by one layer of prismatic 

 cells between the sides of which bridges extend. The intercellular 

 spaces at the surface of these cells are closed by a special cement, the 

 terminal bars. The zona pellucida varies from 1 /x to 17 /x according to 

 the stage of development. During ite growth it is always formed by 

 two or three different elements ; there is a fundamental homogeneous 

 substance filling up the spaces between a system of numerous canals or 

 tubules which enclose filaments or prolongations of the epithelial cells 

 which are connected with the surface of the yolk. The fundamental 

 substance is developed as a cuticular element from the terminal bars or 

 intercellular cement. A secondary network is produced by the superficial 



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

 of the papers abstracted. Tha object of this part of the Journal is to present 

 a summary of Ihe papers as actually puhlishcd, and to describe and illustrate 

 Instruments, Apparatus, etc., which are either new or have not been previously 

 described in this country. 



