484 DAVIDSON BLACK 
motor spino-occipital root being approximately the same in 
Bdellostoma and Petromyzon, and but very slightly reduced in 
Myxine (fig. 8). 
With regard to the absence of the glossopharyngeal nerve in 
Bdellostoma. but little positive evidence can be advanced here. 
The first (rostral) two vagus rootlets indicated in figures 7 and 
8 are so closely associated at both their origin and exrt that 
they should, I believe, be considered as a single root. The 
probability of this is increased when it is noted that the first 
vagus root in Myxine is much larger than the succeeding ones. 
The best evidence on this point, though it be but negative, may 
be had by reference to figure 8. The reduction of the frontal 
portion of the caudal viscero-motor column in Bdellostoma when 
thus compared with Petromyzon is clearly evident, though this 
reduction is apparently not so extensive as in Myxine. 
Such evidence as the above, together with that furnished by 
the similar observations of Rothig and Kappers (88), tends to 
confirm Johnston’s conclusion that the so-called glossopharyn- 
geal nerve in myxinoids is in reality pup a pharyngeal branch 
of the vagus (53). 
With regard to the smallness of the gap between the V—VII 
nucleus and the vagus column in Bdellostoma, this seems to be 
the result of a condensation or ‘telescoping’ of the medulla as a 
whole, probably in consequence of the complete loss in this 
form of the peripheral glossopharyngeal area (vide Johnston, 
53; Stockard, 90). 
Finally, I would point out that the arrangement of the motor 
roots and nuclei in the medulla of Bdellostoma dombeyi is not a 
primitive one. On this account I cannot entirely agree with the 
opinion expressed by Worthington (99, p. 188), and by Ayers 
and Worthington (4, p. 1) to the effect that myxinoids are the 
most primitive craniates known and several degrees lower than 
the Petromyzontes. This conclusion is in harmony with that 
of Réthig and Kappers based on their study of the motor nuclei 
in Myxine (1. ¢.). 
