SUMMARY OF CURRENT RESEARCHES 



RELATING TO 



ZOOLOGY AND BOTANY 



(principally invertebrata and cryptogamia), 



MICEOSCOPY Etc.* 



ZOOLOGY. 



VERTEBRATA. 



a. Embryology, f 



Monochorial Twins.J — -A. Rosner discusses the numerous theories as 

 to the origin of monochorial twins in man, and comes to the conclusion 

 that they arise from a bi-ovular Graafian follicle, whose two ova, liberated 

 together and normally fertilised, are borne to the uterus united by some 

 cells of the discus proligerus, and become surrounded by a common 

 caduca (decidua capsularis, seu reflexa). The chorionic areas which are 

 in contact and form the partition between the two developing ova may 

 disappear, simply because they are not in immediate touch with the 

 nutritive caduca. In other words, the single chorion is the result of the 

 coalescence of two chorions in consequence of deficient local nutrition in 

 the chorionic areas which are in contact. 



It occurred to Rosner that some secure basis for interpretation might 

 be obtained by a study of two well-known mammals, which habitually 

 produce monochorial twin, or rather multiple foetuses. These are two 

 armadillos — Praopus hybridus,§ studied by von Ihering, and Dasypus 

 novemcinctus, § studied by Kolliker, Milne Edwards, Duges, and von 

 Ihering. The first has usually eight foetuses, always of the same sex, 

 and with a common chorion ; the second has four within a common 

 chorion, and also, according to von Ihering, of similar sex. Now, by 

 sectioning the ovaries of Dasypus, Rosner found that many of the 

 Graafian follicles are 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 two most developed contained four each, i.e. the 

 number usually found within one chorion in the pregnant female. 



As the primordial follicles in the ovary of Dasypus, whether foetal 



* 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 published, and to 

 describe and illustrate Instruments, Apparatus. &c, which are either new or have 

 aot been previouslv described in this country. 



t This section includes not only papers relating to Embryology properly so called, 

 hut also those dealing with Evolution, Development, Reproduction, and allied subjects. 



X Bull. Internat. Acad. Sci. Cracovie, No. 8, Nov. 1901, pp. 443-50 (1 pi.). 



§ We keep to Bosner's terminology. 



