280 Miscellaneous. 



furtlipst ndriinced stage of thp younfj Pc/ro)iii/^07i Plancri six weeks nfter 

 hiiti'liiii<;, as figured h\ Schiiltze in' his iiionioir on the development of 

 tliat fish. The figures are magnified to the sjime vertical dimension, so 

 as to afford a means of estimating, roughly, the clianges in the jiropor- 

 tional growth of the various ]iarts of the head of the Lamprey in its ]>ro- 

 gress from the embrvonio towards the adult condition. In C, t lie brain is 

 already differentiated into the three primary vesicles and the vesicles of 

 the cerebral hemispheres, though they are not shown, the whole bniin being 

 merely indicated by the dark shading. The traliecuhv ( 7V), which have 

 already united in front, are indicated, but not the semilunar etlimoidal 

 cartilage, which lies above and Ivhind the nasal sae. 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 Amphioxns) are arranged is 

 shown. "i'lie tentacles of Ampfiioxiis are re]iresented by the tentacles 

 of the Ammr.ccefc. the hood-like "upper lip" of the latter obviously 

 answering to the medi.'n prolongation of the head of AmphioTXS with the 

 two lateral folds of integument which lie outside the bases of the tentacles 

 and are continued bjick into the ventro-lateral ridges. The relative shorten- 

 ing of the notochord, find 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-Op) : 

 and a third [Hy-Hy) pnsses through the region of the auditory sac and 

 hyoidean arch. 1, 2, 3, hyoidean and first and second branchial clefts 

 oi Ammocoefes; r., it., iti , iv.. &c.. myotomes of Amphioxus ; My, mye- 

 lon or spinal cord ; Ch, notochord. 



MISCELLAXEOUS. 

 On the Gammaridae of Lai- e Ba'ilcal. By Dr. B. N, Dtho-wsky. 



This memoir reveals to ns the existence in Lake Baikal of an 

 Amphipodoiis fanna remarkable for an abundance and variety of 

 .specific forms such as we certainly had no reason to expect. 



nerstfeldt, in a memoir published in 18.58, described seven species 

 of Gammarus found in different rivers of Siberia and in Lake BaiTjal. 

 From what we know of freshwater faunas there was not much 

 rea.son to suppose that this number would be greatly augmented ; 

 but Dr. Dybowsky now makes known 97 species of Gammaridae, 

 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. 0. Sars *. In Xorway the freshwater 

 Gammaridffi are represented only by four species ; that is to say, 

 they are only one twenty-fourth the number of those of Lake 



* n. O. Sars, 'Histoire Naturelle de.i Crustac^s d'eau douce de Xor- 

 vege : Malaeo.atrac^s.' Christiania, 1807. 



