230 Miscellaneous. 
furthest advanced stage of the young Petromyzon Planeri six weeks after 
hatching, as figured by Schultze in’ his memoir on the development of 
that fish. The figures are magnified to the same vertical dimension, so 
as to afford a means of estimating, roughly, the changes in the propor- 
tional growth of the various parts of the head of the Lamprey in its pro- 
gress from the embryonic towards the adult condition. In C, the brain is 
already differentiated into the three primary vesicles and the vesicles of 
the cerebral hemispheres, though they are not shown, the whole brain being 
merely indicated by the dark shading. The trabecule (7'’r), which have 
already united in front, are indicated, but not the semilunar ethmoidal 
cartilage, which lies above and behind the nasal sac. In D, neither the 
ethmoidal nor the trabecular cartilages are shown, but the contour of the 
brain is indicated; and the manner in which the longitudinal muscles 
(which represent the anterior myotomes of Amphiorus) are arranged is 
shown. ‘The tentacles of Amphioxus are represented by the tentacles 
of the Ammocete, the hood-like “upper lip” of the latter obviously 
answering to the median prolongation of the head of Amphioxus with the 
two lateral folds of integument which lie outside the bases of the tentacles 
and are continued back into the ventro-lateral ridges. The relative shorten- 
ing of the notochord, and lengthening of that region of the brain which lies 
in front of the origins of the optic nerves, in C, as compared with B, is 
remarkable, 
A line is drawn in all the figures through the anterior margin of the 
nasal sacs (Na—Na) ; another has the same relation to the eyes (Op-—Cp) : 
and a third (Hy-Hy) passes through the region of the auditory sae and 
hyoidean arch. 1, 2, 3, hyoidean and first and second branchial clefts 
of Ammocetes; 1., 11., 111, Iv., &e., myotomes of Amphiorus; My, mye- 
lon or spinal cord; Ch, notochord. 
MISCELLANEOUS. 
On the Gammaride of Lake Baikal. By Dr. B. N. Dynowsxy. 
THis memoir reveals to us the existence in Lake Baikal of an 
Amphipodous fauna remarkable for an abundance and variety of 
specific forms such as we certainly had no reason to expect. 
Gerstfeldt, in a memoir published in 1858, described seven species 
of Gammarus found in different rivers of Siberia and in Lake Baikal. 
From what we know of freshwater faunas there was not much 
reason to suppose that this number would be greatly augmented ; 
but Dr. Dybowsky now makes known 97 species of Gammaride, 
nearly all of which are new. They come almost exclusively from 
Lake Baikal, only a few of them in summer ascending the mouths 
of its tributaries; and there are very few which permanently 
inhabit the rivers. 
We do not think that any region of the globe has furnished a 
contingent of freshwater Amphipoda which approaches this in 
number of species. It is curious, for example, to compare the fauna 
of Siberia, in this respect, with that of Norway, which we know 
from the fine memoir of G. O. Sars*. In Norway the freshwater 
Gammaride are represented only by four species; that is to say, 
they are only one twenty-fourth the number of those of Lake 
* G. O. Sars, ‘Histoire Naturelle des Crustacés d’eau douce de Nor- 
vége: Malacostracés.’ Christiania, 1867. 
