SUMMAEY OF CUKRENT RESEARCHES. 299 



developed villi and young villi exist in the growing intestine side by 

 side ; (3) the villi appear first as longitudinal folds which grow larger 

 and then break up into villi ; (4) the villi develope first in the upper 

 portions of the intestine. 



Placenta of Galago agisymbanus.*— Prof. H. Strahl finds that in 

 this as in other lemurs the placenta is diffuse. In the middle of preg- 

 nancy the villi are scattered over the whole of the chorion, but they do 

 not reach an equal degree of development in its different regions, nor do 

 they arise simultaneously in these regions. The absorptive mechanism 

 of the placenta is somewhat complex ; for three or four different con- 

 ditions obtain. These arise in part in later stages of development, and 

 depend udou variations in the form and arrangement of the chorionic 

 epithelium and the blood-vessels of the villi. The utilisation of the 

 extravasated maternal blood which is to be found in the mucous mem- 

 biane is carried out by the epithelial cells of the uterine glands. 



Presence of a Thymus of the Fourth Visceral Cleft in Man.f — 

 Dr. K. Groschuff, in a previous paper J on the development of the 

 thymus in mammals, came to the conclusion that a thymus segment de- 

 velopes in relation to the fourth gill-cleft wherever this possesses an 

 epithelial body (glandula parathyroidea). In man the fourth gill-cleft 

 regularly gives origin to such an epithelial body, but yet a thymus 

 segment belonging to this cleft has not hitherto been directly observed. 

 A careful investigation of embryos and new-born subjects has proved 

 the existence of this thymus segment in some cases, but has led the 

 author to modify his views to some extent. He does not now regard 

 the thymus segment of the fourth gill-cleft as a constant structure in 

 man, and finds that even in cattle and cats it is not, as he previously 

 thought, invariably present. Generally, he now states his position as 

 follows : — this thymus segment is not invariably present in any mammal, 

 but wherever an epithelial body occurs it may be expected to occur with 

 more or less frequency. 



Double and Bifid Ureters in Mar.§ — E. Sacquepee describes a case 

 of double ureter, and discusses other described cases in their bearing on 

 theories of the development of kidney and ureter. He finds that uni- 

 lateral doubling has been frequently observed ; bilateral doubling, or the 

 presence of two ureters at one side, and a bifid ureter at the other, as in 

 Lis own case, is rare. Most of the existing theories in explanation of 

 these facts fail to explain all the anomalies which occur ; these are, the 

 fact that the ureter is sometimes double and sometimes bifid ; that the 

 abnormal ureter often drains the upper part of the kidney, which is 

 sometimes normal, sometimes much modified ; and that the abnormal 

 ureter may open at one of several points. It is certain that the Wolffian 

 duct may give rise to two ureterine outgrowth?, and this explains some 

 of, but not all, the anomalies which occur. Other cases may be explained 

 by the persistence of the Mullerian duct in the male and the Wolffian 

 in the female, thus producing only an apparent ureter. Again, the 



* Abh. Senckenberg. Naturf. Ges., xxvi. (1899) pp. 153-99 (8 pis.). 



t Anat. Anzeig., xvii. (1900) pp. 161-70 (5 tigs.). 



I Tom. cit, xii. (1896) pp. 497-512. 



§ Journ. Anat. Physiol., xxxvi. (1900) pp. 103-20 (4 figs.). 



