502 JULIA B. PLATT. 
The original epibranchial ridge to which the infra-orbital 
line dates its origin is hardly less primitive. In fact, the otic 
part of the system which Ewart views as the primitive, undi- 
vided part of the severed infra- and supra-orbital lines, is, in 
Necturus, itself cut off from the infra-orbital ridge very shortly 
before the stage represented in fig. 1. 
The description given by Mitrophanow! (29) of the develop- 
ment of the supra- and infra-orbital lines in Acanthias accords 
better with Ewart’s prognostication, inasmuch as Mitrophanow 
finds that these lines grow in directions nearly at right angles 
to one another from a thickening of the ectoderm above and 
anterior to the hyomandibular cleft; but Mitrophanow also 
finds that the thickening connected with the otic nerve takes 
its rise from the infra-orbital line. It consequently cannot 
be viewed as representing in Acanthias the undivided rudi- 
ment from which the supra- and infra-orbital lines have 
parted. 
Mitrophanow does not mention the early connection of the 
primitive supra-orbital ridge with the trigeminal ganglion and 
ramus ophthalmicus profundus, nor does he lay stress on the 
extensive additions which the peripheral nervous system re- 
ceives from the skin along the lines of ectodermic thickening. 
In fact, instead of viewing the skin as the source of the sensory 
nerves, the author speaks of the branchial sense-organs above 
the first and second branchial clefts as following in their 
development the small supra-branchial branches of the glosso- 
pharyngeal and vagus nerves; and again, in stating his con- 
clusions (loc. cit., p. 211) Mitrophanow says of the several 
branchial sense-organs that “leur formation est simultanée 
avec le développement des petites branches nerveuses supra- 
branchiales.” Evidently the author does not recognise the 
precedence of the sensory ridge. 
Since Mitrophanow claims as the result of his study that the 
segmentation of the lateral line system is entirely secondary, I 
shall be interested to discover when I again have my Acanthias 
material with me whether traces of the primitive segmentation 
1 T regret that the Russian publications of this author are inaccessible to me. 
