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polymeric vagus that they may be termed with some right 
ventral vagus roots, as has been done by GEGENBAUR. 
Better still would it be, no doubt, to speak of ventral 
accessorius roots or vago-accessorius roots, for the acces- 
sorius originates in closest connection with the anterior 
rudimentary ganglia behind that of the primary vagus. In 
Selachians it still forms part of the vagus which here 
innervates also the Musculus trapezius, one of the muscles 
in the branchial region, which originate from the lateral 
plate and are innervated by the dorsal nerves of the head. 
The strong development of this muscle in higher Vertebrates 
causes the accessorius to split off from the vagus. 
Hypoglossus homologous in Vertebrates? — ls the hypo- 
glossus homologous in the different groups of Vertebrates ? 
| think this question must be answered in the affirmative. 
Truly, its roots belong to segments bearing different numbers 
in different groups and still more do their relations to the 
skull vary. The first circumstance, however, as has been 
argued recently in a thorough way by GOODRICH (1914), 
is no hindrance to considering structures as homolo- 
gous. On the contrary, homology is quite independent 
from metameric segmentation and only secondarily can there 
be established a more or less fixed relation between 
both, especially in forms with a restricted number of 
segments, and at the anterior end of the body, e.g. In 
the anterior segments of the head and their organs in 
Craniates. Were we to make homology dependent upon 
the number of the segments from which the organs arise, 
then there could be no question of an homology of the 
paired limbs among fishes and tetrapods, as the segments 
from which they arise are by no means the same and 
subject to considerable variation both in number and in 
situation. The same holds e.g. for the pronephros. In 
Urodelan Amphibians the first pronephric funnel is found 
in the second segment behind the skull (FIELD, 1891, 
p. 261, GOODRICH, 1911, p. 112), ie. in segment nr. 7 
which in Selachians and Amniotes belongs to the skull. 
In the latter groups the first funnel is found as a rule 
in the third segment behind the skull, i.e. in segment 
about nr. 11 (FRORIEP, 1905, p. 119). Nobody will doubt 
the homology of these organs. The “segmental level 
to which they belong may shift forwards and backwards, 
extend over a greater or over a lesser number of segments 
