694 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
the anus only arises by a later breaking through ; in the Urodela, on the 
other hand, the most ventral part of the blastopore never closes. The 
formation of the anus of the Anura is therefore subject to secondary 
modification. The recent work of Prof. Gotte supports this view. 
Development of Kidneys in Fat-Bodies in the Frog.* — The following 
is a summary of the results of the studies of Prof. A. Milnes Marshall 
and Mr. E. J. Bles, on the development of the kidneys in fat-bodies of 
Bana temporaria. The head-kidney and its duct are mesoblastic struc- 
tures, in the formation of which the epiblast takes no part ; but the 
cloacal openings of the ducts are formed partly by outgrowth from the 
gut. In early larval life the head-kidney is a large and complex organ, 
but it begins to degenerate in tadpoles about 20 mm. in length. The 
first stage in its degeneration is the great and irregular dilatation of the 
tubules, accompanied by the destruction of their epithelial lining ; this 
is apparently due to the blocking of the archinephric duct. Ultimately 
the head-kidney disappears completely, its three nephrostomes closing 
up and undergoing atrophy. The peritoneal opening of the oviduct is a 
new formation, and not a persistent nephrostome. The tubules of the 
Wolffian body begin to form shortly before the head-kidney degenerates, 
they develope from behind forwards, and are at first segmentally 
arranged ; they are formed from the mesoblast between the aorta and 
the - archinephric ducts, and arise independently of the peritoneum. 
Nephrostomes are formed at an early period, and open into the body- 
cavity. The fat-bodies are formed from the anterior ends of the genital 
ridges. 
Development of Blood-vessels of Frog.j — Prof. A. Milnes Marshall 
and Mr. E. J. Bles have studied the development of the blood-vessels in 
Bana temporaria. As to the heart, they found that it is developed 
before any of the vessels of the visceral arches, and before the dorsal 
aortse. The muscular wall of the heart is formed from the splanchnic 
layer of mesoblast ; the inner or endothelial wall is derived directly 
from the hypoblast of the ventral wall of the pharynx and of the 
hepatic diverticulum. The heart is from the first in connection at its 
posterior end with the veins of the yolk-sac and of the liver ; its several 
chambers become marked off by constrictions before its anterior end 
acquires any connection with blood-vessels. The apparent thickening of 
the wall of the ventricle is due to the development of an internal muscular 
reticulum, and the absence of nutrient vessels in this wall is explained by 
this arrangement. The valves of the truncus arteriosus are established 
before the metamorphosis. The blood-vessels arise as irregular lacunar 
spaces in the mesoblast, and these spaces open into each other and so 
form continuous channels. The mesoblast-cells surrounding the 
channels become converted into the epithelial walls of the vessels. The 
further growth of the vessels is sometimes effected by the formation of 
solid cellular cords, continuing the lines of the vessels. The axial cells of 
the cord break down and so give rise to tubular vessels. Blood-corpuscles 
are at first absent ; when they do appear they are formed from the walls 
* Studies from the Biol. Lab. Owens Coll., ii. (1890) pp. 133 58 (1 pi.). 
t T. c., pp. 185-268 (3 pis.). 
