172 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
the ventral trunk-line develops. The anterior part of the primitive 
ventral longitudinal ridge is retained in the ventral part of the hyo- 
mandibular line of sense-organs (the internal mandibular). The lateral 
lines of the trunk grow from the head backwards through indifferent 
ectoderm, and do not result from the direct modification of primitive 
ridges. 
(3) The primitive ridges are the source of both nervous and con- 
nective tissue ; the secondary, of nervous tissues only. 
(4) The primitive ridges of the trunk, as of the head, add to the 
meseetoderm. 
(5) Few of the cells that disappear from the secondary ridges of the 
trunk, as the sense-organs arise, enter the lateral nerve. The majority 
migrate between the two layers of the ectoderm towards the terminal 
point of growth in the advancing line. 
(6) The third vagus-cleft forms in the intersegmental plane once 
occupied by the second vagus-cleft, and the primitive vagus myotome 
divides in the plane secondarily occupied by the second vagus-cleft, 
while the nerves of the second vagus-arch arise from the root of those 
of the first arch. This suggests the interpolation of a vagus-segment 
in the original metamerism. 
(7) Some fibres from the lateral-line ganglion enter the vagus-root, 
but most enter the brain through the glossopharyngeal root, via the 
neural crest-cells bridging the space between the vagus and glosso- 
pharyngeal ganglia. 
(8) Many cells of the neural crest of the trunk help to form con- 
nective tissue, not spinal ganglia. 
(9) Motor nerves of the trunk appear before spinal ganglia, by 
migration of bipolar cells from the cord. 
(10) The nerve below the infra-orbital sensory line divides into two, 
connected with the Gasserian and facial ganglia respectively. 
(11) The ramus hyomandibularis and its direct continuation, the 
internal mandibular, appear as the post-trematic branch of the hyoid 
arch, while the hyoid nerve resembles the lateral nerves of the posterior 
arches. 
(12) Cells of ectodermic origin contribute to form blood-corpuscles 
in the branchial region. 
(13) A common reticulum, such as Sedgwick describes, into which 
nuclei migrate, does not exist in Necturus, although delicate protoplasmic 
prolongations connecting cell with cell imitate the specialised co-ordi- 
nation of the nervous system. 
(14) The root of the sensory nerve is no index to the segmental 
value of the nerve. 
Thyroid Gland and Supraperieardial Bodies in Necturus.* — Miss 
J. B. Platt finds that the development of these bodies in Necturus , which 
she has studied, differs from that in Triton or Siredon , as described by 
Maurer, in the following respects : — 
(1) The thyroid outgrowth begins at the hyomandibular, not at the 
second branchial pocket ; 
(2) The cells separated from the anterior part of the outgrowth 
* Anat. Auzei°:., xi. (1S96) pp. 557-67 (9 hgs.). 
