356 RUTH B. ROWLAND 
of the excretory system with a study of both the structure and 
the function of this organ in its fully formed state. The head 
kidney of Bdellostoma is shown to be a composite structure, 
possessing at its earliest appearance all the characteristics of a 
pronephros, with the single exception of the typical glomerulus, 
but later fusing with the anterior end of the mesonephros and 
losing all connection with the exterior. Structurally, then, the 
head kidney in at least one of the myxinoids is rendered incap- 
able of playing the role of an excretory organ, but since it is 
connected with both coelomic cavity and the circulatory sys- 
tem, and since, also, it has been proved possible to transfer 
certain substances from the coelomic fluid directly into the cir- 
culation. Price concludes that its probable function is the trans- 
ference of lymph from the body cavity into the blood-vessels. 
Since the discovery of the organ by Johannes Mliller ('29), 
the origin, development and morphology of the amphibian 
pronephros have been described by many investigators, chief 
among whom are von Wittich ('52), Fiirbringer ('78 a), and Field 
('91). An excellent review of the early controversies concerning 
its structure is also given by Field. The presence of a well- 
developed pronephros in the amphibian embryo, its early appear- 
ance, and its relatively large size have led to the general assump- 
tion that it is a functioning organ. Its characteristic structure, 
consisting in a glomerulus which extends freely into the coelomic 
cavity, a coiled tubule furnished with open ciUated funnels for 
the intake of coelomic fluid, and a simple duct estabUshing 
direct connection with the exterior, further points to its function 
as excretory in nature. Still, from the physiological viewpoint, 
no experimental evidence as to the extent to which the embryo 
is dependent upon it for the elimination of excretory products 
had been offered at the time of pubUcation of my first note ('16) ; 
Since then Swingle (19), working independently upon the embryo 
of Rana sylvatica, has obtained results which in the main agree 
with my own. 
In the series of experiments described in the present paper, 
the necessity of these organs for the life of the embryo has been 
proved by the fact that death follows, in time, after the removal 
