134 PROFESSOR MARSHALL AND EDWARD J. BLES. 



anterior end of the trunk, immediately ventral to the muscle- 

 plates. This fold is at first ill defined dorsally, but sharply marked 

 along its lower or ventral edge. At a slightly later stage the fold, 

 which lies immediately beneath the epiblast, becomes more clearly 

 marked off from the rest of the mesoblast, and its communication 

 with the ccelom or body cavity becomes reduced to a narrow 

 longitudinal slit confined to its anterior end, extending along 

 about three myotomes. The hinder part of the fold forms a tube 

 which extends backwards towards the cloaca, lying between the 

 epiblast and somatopleuric mesoblast. By further changes, the slit- 

 like aperture of communication with the ccelom becomes divided 

 by constrictions into three tubular openings, which become the three 

 nephrostomial apertures characteristic of the Anuran head kidney. 



The longitudinal tube into which the three nephrostomies open, 

 become twisted on itself like a letter S, and become further com- 

 plicated by the development of lateral diverticula from the limbs of 

 the S ; the complicated and convoluted tubular mass so formed 

 constituting the head kidney. The hinder part of the tube continues 

 its growth backwards, and soon acquires an opening into the cloaca. 



Goette notes further that the ccelom first becomes a conspicuous 

 cavity opposite to the head kidney, and that into this cavity the 

 glomerulus projects on each side as a thick walled lateral diverticulum 

 from the aorta. Later on the ccelom extends ventralwards round 

 the sides of the body by separation of the somatopleuric and 

 splanchnopleuric layers of the mesoblast from each other. At a still 

 later stage, when the lungs have attained some size, the part of the 

 coelom opposite the glomerulus and the nephrostomes becomes again 

 marked off, though not completely separated from the rest of the 

 body cavity, by fusion of the outer surface of the lung with the 

 somatopleure at the level of the head kidney. 



Fiirbringer,* in his admirable account of the development of the 

 Amphibian kidne}^, gives a useful summary of the work- done by 

 previous investigators, and a careful description of the mode of develop- 

 ment of the head kidney and its duct in Ram temporaria, as well 

 as in Salamandra and other Amphibians. He agrees in the main with 

 Goette, but corrects him in certain points, and adds a number of 



* Fiirbringer, "Zur Entwickelung der Amphibienniere," Heideberg, 1877, pp. 13-32. 



