ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
153 
is fully described, and an attempt is made to determine which portion 
of the embryo is derived from the cells proliferated from the primitive 
streak. 
Fusion of Epiblastic Layers in Rabbit and Frog.* — Mr. R. Assheton 
points out that in the Frog as well as in the Rabbit there is a fusion 
of two epiblastic layers. He gives an account of what may be seen in 
Rana temporaria. With regard to the pigmentation of the cells in the 
Frog, he points out that, as pigment is present in the unfertilized egg, 
as a superficial layer covering the upper pole, we find that the superficial 
layer of cells after segmentation is more deeply pigmented in the more 
internally situated segments. Secondly, the pigment seems to be in 
some way connected with actual protoplasmic activity, as it appears 
internally wherever the division of cells takes place. Although his 
evidence is, he allows, very far from being conclusive, Mr. Assheton 
thinks that it points very strongly towards the inference that the 
epidermic layer or epiblast in the Frog gives rise to the spongioblastic 
elements, and the nervous layer to the neuroblasts. A brief comparison 
is instituted between the Rabbit and the Frog. 
Development and Structure of the Whale. | — Under this title 
Drs. G. Guldberg and F. Nansen publish a beautifully illustrated 
volume containing several essays on various Cetacea. After a historical 
survey of our knowledge regarding the development of the Whale, the 
development of Lagenorhynchus acutus is discussed. Of this whale they 
were so fortunate as to obtain an embryo no more than 8 mm. long ; it 
was remarkable for its already long tail. Embryos 26 and- 30 mm. long 
were at first sight regarded as distinctly mammalian, but closer con- 
sideration showed that the Cetacean type had, even at this stage of 
development, set its peculiar stamp upon these embryos. The relatively 
great distance between the nasal and the oral apertures, the external 
nasal apertures fused into one transverse cleft, the short neck and the 
long tail, the absence of external ears and external hind extremities, 
while the fore extremities are already well developed, mark the embryo 
as Cetacean. The characteristics of the class and order are thus even 
at this stage intermingled, and we do not, as we are ordinarily taught 
to suppose, see only general or phylogenetic characters. The authors 
appear to be much struck by this, but our readers will probably re- 
member Mr. Sedgwick’s essay on Von Baer’s law.J Put into a few 
words, they say the embryo seeks by the most direct way to attain to 
the likeness of its parents. There is a short notice of L. albirostris , the 
smallest foetus of which measured 720 mm. In it the distribution of 
colour was already so strongly marked that several of the specific 
characters were disclosed. The development of the common Porpoise 
is discussed in greater detail ; the powerful development of the tail at 
an early stage leads to the expression of the general law that an organ 
which plays a conspicuous part in the independent existence of the 
animal appears early, and even in its first embryonic development grows 
rapidly and assumes a more or less prominent position. An embryo 
* Quart. Journ. Micr. Sci., xxxvii. (1894) pp. 165-71 (1 pi.). 
t Bergens Museum, v. (1894) large 4to, 70 pp., 7 pis. and 6 figs. 
t See this Journal, 1894, p. 433. 
