THE REGION OF THE SPINAL CORD AIQ 
to excrete to the exterior? What should we look for in our search 
after the lost coxal glands ? 
The answer to these questions is most plainly given in the case 
of the pronephros, especially in Myxine, where Maas has been able 
to follow out the whole process of the conversion of nephric tubules 
into a tissue resembling that of a lymph-gland. 
He states, in the first place, that the pronephros possesses a 
capillary network, which extends over the pronephric duct, while 
the tubules of the mesonephros possess not only this capillary net- 
work, equivalent to the capillaries over the convoluted tubules in the 
higher vertebrates, but also a true glomerulus, in that the nephric 
segmental arteriole forms a coil (Knauel), and pushes in the wall of 
the mesonephric tubule. He describes the pronephros of large adult 
individuals as consisting of— 
1. Tubules with funnels which open into the pericardial ccelom. 
2, A large capillary network (the glomus) at the distal end. 
3. A peculiar tissue (the ‘ strittige Gewebe’ of the Semon-Spengel 
controversy), which Spengel considers to be composed of the altered 
epithelium of pronephric tubules, while Semon looks on it as an 
amalgamation of glomeruli. 
Maas is entirely on the side of Spengel, and shows that this 
peculiar tissue is actually formed by modified pronephric tubules, 
which become more and more lymphatic in character. 
He says: “The pronephros consists of a number of nephric 
tubules, placed separately one behind the other, which were origi- 
nally segmental in character, each one of which is supplied by a 
capillary network from a segmental branch of the aorta. The 
tubules begin with many mouths (dorso-lateral and medial-ventral) 
in the pericardial cavity; on their other blind end they have lost 
their original external opening, and there, in the cranial portion of 
the head-kidney, before they have joined together to form a collecting 
duct, they, together with the vascular network, are transformed into 
a peculiar adrenal-like tissue. The most posterior of the segmental 
capillary nets retain their original character, and are concentrated 
into the separate capillary mass known as the glomus.” 
Later on he says: “Further, the separate head-kidney is more and 
more removed in structure from an excretory organ in the ordinary 
sense. One cannot, however, speak of it as an organ becoming rudi- 
mentary; this is proved not only by the progressive transformation 
