liiSg.] Physiology. 173 
itive constitution of motor nerves, neither fibres nor sheaths 
form a part. Neither are axis cylinders or medullary substance 
developed. End-organs or terminal branching ramifications 
of the nerve fibres do not as yet exist, but the capacity for their 
development is probably inherent in the simple structures and 
relations above described. The relations described by Dohrn 
are strongly opposed to the theory of the ab initio continuity 
of nerve and muscle by impalpably fine fibres, and if fully es- 
tablished fatal to Hensen's doctrine. It is needless to add that, 
while these new results are not wholly in accord with those of 
Balfour, they will probably serve to complete the true doctrine 
of the development of the spinal and cranial nerves, the founda- 
tions of which were first laid down by that remarkable investi- 
gator. 
The Maturation and Fertilization of the Egg of 
Petromyzon Planeri.^ a. a. Bohm in this extended mem- 
oir gives a very complete resume of the work of his predeces- 
sors upon the early history of the eggs of the lamprey. The 
formation of the polar globules is described, and the peculiar 
manner of union of the segments of the female and male pro- 
nuclei are illustrated. It seems that the chromatin substance 
of the head of the spermatozoon in this process always first 
breaks up into about four rounded segments or spermatomerites 
as Bohm calls them, which remain for some time lying close to- 
gether in a straight or curved row. 
PHYSIOLOGY.^ 
Inhibition in Mammalian Heart.— Professor McWilliam 
continues" his work on cardiac physiology by a study of the 
phenomena of inhibition in the mammalian heart.* The results 
are given in considerable detail, and can be discussed here very 
briefly only. The efifects of the stimulation of the vagus nerve on 
theauricles and on the ventricles are in general similar.consisting 
'^Ueber Reifung und Befruchtiing ctes Eies von Petromyzon planeri. Arch. f. 
mik. Anat., xxxii. 4 Hft. i88«. pp. 613—670. Taf. xxiv— xxv. 
^This department is edited by Dr. Frederic S. Lee, Bryn Mawr College, 
Bryn Mawr, Pa. 
^See American Naturalist, Jan. 1889. 
* Journal of Physiology, vol. 9., p. 345. 
