247 
that they can no longer be distinguished from each other 
From the exact place, however, where the lateral placode of the- 
N. facialts was formerly found, spring the sensory branches: 
of the facíialis, the ramus ophthalmicus superficialis, the 
ramus buccalis and mandibularis. These innervate the cranial 
part of the lateral line system and, according to KLINKHARDT, 
grow out from the lateral placode of the latter in the same- 
way as the ramus lateralis of the vagus, i.e. within the 
ectoderm, intraepithelially. 
The obvious inference, therefore, is, that ín these banale: 
of the lateral sense-organs we have to look for the lateral 
or parapodial ganglia of Annelids, which accordingly have 
been lost in the trunk and preserved only in the segmented 
region of the head, which in more than one respect exhibits 
primitive features. The advantages of this conception over” 
that of EISIG will be evident. Just as with the ganglia of the- 
lateral sense-organs in Annelids, the dermatogenetic ganglia 
of the Vertebrate head arise in close connection with 
epidermal sense-organs, while the spinal ganglia have- 
no primary relation whatever to them. The segmental 
communications of the spinal ganglia with the lateral sense- 
organs have only been preserved in the head, in the trunk 
they have been replaced by the collector. To thís conception 
the presence of a segmental connection of the spinal ganglia 
with the corresponding organs of the lateral line, as described 
in Petromyzon by JULIN (1887) and ALCOCK (1899), but denied 
by DOHRN (1888, and FüRBRINGER (1897), would no doubt 
be a valuable support. Similar connections were found by 
HOFFMANN (1901, p. 39, 45) in Urodelans and described and 
illustrated by him in a very positive way as regular anasto- 
moses of the dorsal branch of the 5tt — 20t* spinal nerves- 
with the ramus lateralis vagi. 
As to the epibranchial fusion of the dorsal cranial nerves- 
with the epidermis, | can only suppose with BEARD (1885) - 
that it has arisen in connection with the gill-slits to which 
it shows such close relations. FRORIEP (1891, p. 63) has 
pointed to the close connection between the epibranchial 
ganglia and the rudiment of the thymus, a connection which, 
however, gets lost in the adult state. In no case have these 
branchial sense-organs been found to persist in the adult. 
Different theories on the metameric structure of the head. — 
As already observed, the theory advanced here appears to 
