ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
171 
ment of the vesicle from the skin is due to the differentiation of the 
subcutaneous tissues and the formation of the pigment membrane. 
The brain undergoes an eversion which thrusts it ventral ward and 
lateralward toward the vesicle. But there is also a dorsal shifting of 
the ear vesicle throughout the first month. This may be due to the 
dorsal portions growing more rapidly than the ventral portions. It 
looks as if there were some determinative attraction between the 
endolymphatic sac and the medullary roof to which it invariably 
becomes intimately attached. J. A. T. 
Transplanting Part of Neural Tube of Larval Amblystoma. — 
H. L. Wiemann ( Journ . Exper. Zool ., 1922, 35, 163-88, 18 figs.). 
When a small section of the neural tube, at the stage of the closed 
neural folds, is removed at the level of the second to fourth somites, 
together w 7 ith portions of adjacent somites, and re-implanted at right 
angles to its normal position, the transplanted tube continues its 
development and retains its original polarity. The growing brain pushes 
the anterior stump against the anterior side of the transplanted tube, 
and this may be a factor in forming a union at the point of contact. 
Nerve fibres grow back from the anterior stump into the transplant ; 
the posterior stump becomes club-shaped, but shows no initial tendency 
to send out fibres forward into the transplant. A connexion between 
the transplant and the posterior stump is brought about by the con- 
tinued growth backward of fibres from the anterior stump through the 
transplant. Ascending fibres then grow forward from the posterior 
stump. The transplant eventually becomes absorbed in the reconstructed 
neural tube, but sections 30 to 40 days after the operation showed that 
the cells had not lost their original polarity. When the operation is 
performed at a stage just before the larva becomes sensitive, the process 
is the same, but the union is more rapid. When the operation is 
performed at the earlier stages, but in the region of the fifth and sixth 
somites, or further back, a longer time is required for the formation of 
nervous connexions; out of twelve operations no case of complete 
connexion occurred in 30 days ; in one case at least the transplant was 
disintegrated at the end of 30 days. J. A. T. 
Nerve-Connexions in Transplanted Limbs of Larval Amblystoma. 
— S. B. Detwiler {Journ. Exper. Zool ., 1922, 35, 115-61, 32 figs.). 
Shifting the position of a fore-limb rudiment, a given number of body- 
segments anterior or posterior to its normal site does not effect to the 
same extent a corresponding shifting of the segmental nerve contribu- 
tion to the brachial plexus. There is a marked tendency for transplanted 
limbs to receive innervation from the normal limb level of the cord. 
The evidence suggests that there exists between the limb and its normal 
nerves a developmental relationship which is more intimate in cha- 
racter than that between these same nerves and any other structures. 
The contention is thus supported that mechanical influences, although 
governing in large measure the character of nerve pathways, do not 
reveal how it is that the proper nerve-connexions are made at the 
periphery. J. A. T. 
