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THE AMERICAN NATURALIST [A'ol. XLI 



correspond essentially with the jugular sacs of the pig, rabbit, and cat. 

 Each sac apparently communicates with the veins by a remarkably 

 small opening which was not shown in the model. Dr. Thyng ex- 

 hibited also models of the dorsal and the ventral pancreas in the 

 rabbit, cat, and pig, one model of the latter including a well developed 

 accessory pancreas. 



Professor T. G. Lee of the University of Minnesota was the first to 

 study the implantation and early development of the Sciuromorpha, 

 the suborder of rodents which includes squirrels, chipmunks, prairie 

 dogs, and gophers. Representatives of the other three suborders of 

 rodents have been studied by other investigators. The Sciuromorpha 

 have a characteristic early development. Before the placenta has 

 formed, the vesicle acquires a temporary uterine attachment by means 

 of a knob-like proliferation of cells on its ventral surface. Geomys 

 hursarius, the pocket gopher, which belongs to a distinct family, 

 perforates the epithelium of the uterus and develops in the uterine 

 connective tissue. The aperture in the epithelium does not become 

 closed as in the guinea pig, nor plugged as in man, so that Geomys 

 is said to differ "in certain respects from any other mammal yet de- 

 scribed." It may be noted that in the syncytial covering of the vesicles 

 of all the Sciuromorpha the cells divide only by amitosis. Professor 

 Lee exhibited a few of the interesting sections from his extensive series. 



Dr. M. Herzog of Chicago has studied a very young human embryo 

 in process of implantation. The sections exhibited were similar to 

 those figured by Dr. Peters in 1899 as "the earliest known stage of 

 human placentation." Because of their good condition and the rarity 



i^ndividual who was accidciitally and almost instantly killc(i upon the 

 street; for such material it is tniusiiully W(>11 i)rcscrvc<l. Dr. Herzog 

 has completed the study of the chorion and will soon finish that of the 

 embryonic area and its appendages. The results will probably be 

 published in the American Journal of Anatomy. 



Cytology.— Dr. F. E. Botezat of the University of Czcrnowitz, 



