IN THE EMBRYO CHICK. 621 



they are continuous with the walls of the grooves) partially con- 

 stricted off from the germinal epithelium. The ridges, in fact, 

 now form ducts situated in the stroma of the ovarian ridge, in 

 the space between the Wolffian duct and the germinal epithe- 

 lium. The duct continuous with the last groove is somewhat 

 longer than before. In a general way, the head-kidney may now 

 be described as a duct opening into the body-cavity by three 

 groove-like apertures, and continuous behind with the rudiment 

 of the true Miillerian duct. Although the general constitution 

 of the head-kidney at this stage is fairly simple, there are a few 

 features in our sections which we do not fully understand, and 

 a few points about the organ which deserve a rather fuller 

 description than we have given in this general sketch. 



The anterior groove (Nos. i 3, series B, PI. 27) is at first 

 somewhat separated from the Woiffian duct, but approaches 

 close to it in No. 3. In Nos. 2 and 3 there appears a rod-like 

 body on the outer side of the walls of the groove. In No. 2 

 this body is disconnected with the walls of the groove, and even 

 appears as if formed by a second invagination of the germinal 

 epithelium. In No. 3 this body becomes partially continuous 

 with the walls of the groove, and finally in No. 4 it becomes 

 completely continuous with the walls of the groove, and its 

 lumen communicates freely with the groove 1 . 



The last trace of this body is seen on the upper wall of the 

 groove in No. 5. We believe that the body (rj represents the 

 ridge between the first and second grooves of the earlier stage ; 

 so that in passing from No. 3 to No. 5 we pass from the first to 

 the second groove. The meaning of the features of the body r t 

 in No. 2 we do not fully understand, but cannot regard them as 

 purely accidental, since we have met with more or less similar 

 features in other series of sections. The second groove becomes 

 gradually narrower, and finally is continued into the second ridge 

 (No. 8). The ridge contains a lumen, and is only connected 

 with the germinal epithelium by a narrow wall of cells. A 

 narrow passage from the body-cavity leads into that wall for a 

 short distance in No. 8, but it is probably merely the hinder end 

 of the groove of No. 7. The third groove appears in No. 11, 



1 A deep focus of the rather thick section represented in No. 3 shewed the body 

 much more nearly in the position it occupies in No. 4. 



