3l6 JOURNAI. OF COMI'AKATIVE NeUROLOGY. 



ment of the cranial nerves, I pass on to their description in 

 young Ammocoetes, which, when fixed (sublimate, alcohol), 

 measure 3^-3^ mm. While living they might have been 

 fully 4 mm. The stage of development of these specimens, 

 upon which I base mv description, is as follows: There are 

 seven pairs of gill pouches present; the hindermost (eighth) 

 pair is in formation. In the foremost, obliquely placed and 

 temporary pair of pouches, the withdrawal of the endoderm 

 from the epidermis has already taken place and the meso- 

 derm interposed. The diaphragms in the pouches are not 

 yet formed; outer spiracles are still wanting throughout. 

 The septum between the oral cavity and the branchial gut is 

 not yet perforated, but is thinned, and the formation of the 

 stomodcBum from pouches, described by Dohrn,(') whereby 

 the free surface of the velum is enlarged, has set in. There 

 is as yet no pigment in the eye, the lens is constricted off, 

 and the recessus labyrinthi extends dorsad to the exit of the 

 roots of the facial. There exist three pronephric canals with 

 funnels formed, and on each side a large glomerulus. The 

 pronephric duct reaches the hind gut. 



BRANCHIAL SYSTEM. 



I begin with the description of the branchial system of 

 the cranial nerves of this larva, referring to Fig. S, which is 

 drav^^n from three sagittal series of sections, and shows the 

 roots, ganglia and peripheral nerves of the system projected 

 on the median plane. One sees in the figure two rows of 

 ganglia, i.e., dorsally the row of huge or principal (Haupt- 

 ganglion) ganglia (I-V), and ventrally, over the gill septa 

 (gill arches), the epibranchial ganglia (1-12) bound by com- 

 missures into one cord. A third row of ganglia is shown in 

 the drawing between the gill pouches. 



1. Rcoion of the Trigctuirms. — The two principal ganglia 

 of this region are plainly set oft' from each other. The first 



I DoHKN, XII, "Studies," 1888, p. 238-239. 



