and Laboratory Methods. 2059 



CYTOLOGY, EMBRYOLOGY, 



AND 



MICROSCOPICAL METHODS. 



AGNES M. CLAYPOLE, Throop Polytechnic Institute. 



Separates of Papers and Books on Animal Biology should be sent for Review to Agnes M. Claypole, 



55 S. Marengo Avenue, Pasadena, Cal. 



Morgan, T H. The Dispensibility of Gravity Rqux's experiments on the frog's egg 

 in the Development of the Toad s Egg. '^ o oo 



Anat. Anz. 21 : 313-316, 1902. apparently showed gravity acting in a 



definite plane not to be necessary for 



the development of the egg. Other authors have disagreed with these results, but 



the present work confirms them as to the toad's egg. A rubber tube connected the 



water tap with a long glass tube, the latter was made to reach nearly to the 



bottom of a glass jar (450 x 50 c). Water turned on carried the mass of eggs 



round in a most irregular way, rotating them once in 5 to 15 seconds. The toad 



was killed and eggs with sperm put in small jars that were kept stirred, rapidly 



and irregularly, for half an hour. Then they were put into the jars described 



above. The cleavage of such eggs removed in the two-cell stage (after 5 hours) 



was normal, also after 25, 36 and 48 hours. Those removed after several days' 



rotation also produced normal embryos. From these observations it is concluded 



that gravity need not be a determining factor in the development of a bilateral 



plane in the apparently radically symmetrical egg. a. m. c. 



Rosoer A. Monochorial Twins. Bull. Inter- ^f^g^ discussing the numerous theories 

 nat. Acad. Sci. Cracovie, 8: 443-450, pi. i, ... 



1901. (Review in Jour. Roy. Mic. Soc. 159- of monochorial twins in man, the au- 

 160, 1902.) ^^^^ concludes that they arise from a 



bi-ovular Graafian follicle ; the two ova, liberated together and normally fertilized, 

 are united together by some cells of the discus proligerus and become surrounded 

 by a common caduca. The chorionic areas which are in contact and form a 

 partition between the two developing ova may disappear simply from malnutri- 

 tion. Rosner studied animals habitually producing monochorial twins or rather 

 multiple foetuses. The two armadillos, Praopiis hybridus and Dasypus novemcinc- 

 fiis, were chosen. The first usually has eight fcetuses, always of the same sex 

 and in a common chorion ; the second has four under similar conditions. Sec- 

 tioning ovaries of Dasypus, Rosner found many of the Graafian follicles to be 

 pluri-ovular. Out of 52 follicles, 22 contained more than one ovum ; of these, 11 

 had 2, 7 had 3, 2 had 4, 1 had 5, and 1 had 7. The primordial follicles in the 

 ovary of Dasypus, fcetal or adult, contain but one ovum and Rosner shows that 

 several of these fuse to form the pluri-ovular follicle ; each ovum is normally fer- 

 tilized, each develops a chorion of its own, but within the investments of the 

 caduca the chorionic partitions are dissolved till but one chorion remains. That 

 the mono-chorial fcetuses are always of the same sex is interpreted as due to 

 similarity of environment from the Graafian follicle onwards. a. m. c. 



