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SUMMARY OF CURRENT RESEARCHES RELATING TO 
less than 17 mm. long was perhaps more remarkable for the vanishing 
remnants of its hind extremities. With regard to the rudiments of hind 
limbs, it seems that they appear in the Delphinidae as oval, rounded 
paddle-like organs at a stage when the visceral clefts are still distinct. 
Their position on each side of the body corresponds exactly with the 
place where the external commencement of hind limbs generally appears 
in the higher Yertebrata. From the very beginning they are small, they 
are soon left behind in development and undergo rapid retrogression ; 
as they disappear the Cetacean characters appear. So small indeed are 
these appendages that we may be allowed to doubt whether any true 
Cetacean ancestor ever had hind limbs in use. The Killer ( Orca 
gladiator ) is the subject of the next essay. In it the generic and specific 
characters appear to be developed earlier than in any other Odontocete. 
It is remarkable that in a foetus hardly one-fifth the length of the 
newly-born animal, the generic characters are distinctly marked. When 
the foetus attains to half its full size the specific characters are distinctly 
visible, even to the distribution of colour. The foetal membranes of the 
Odontoceti form the subject of the next essay ; they have been observed in 
L. acutus , Orca gladiator , and Phocsena communis (the common Porpoise). 
Finally, the duration of pregnancy is discussed. L. acutus would appear 
to carry its young for about ten months. As to L. albirostris no certain 
conclusions can be drawn. The female 0. gladiator would appear to be 
gravid for about a year, while the common Porpoise carries its young a 
month or two less than the year. 
Blood of Embryo Chick.* — Dr. C. S. Engel shows that the elements 
of the embryo chick’s blood are very different from those in the adult. 
The first blood-corpuscles are nucleated cells, rich in haemoglobin, 
larger than red blood-corpuscles and spherical, and with a large nucleus 
which often shows nuclear segmentation. They are metrocytes of the 
first generation, and on the fourth or fifth day they give rise to a second 
generation. These daughter-cells do not divide by karyokinesis, but 
have sometimes several nuclei. From the fifth day onwards they divide 
into (1) a nucleated portion with associated pigmented protoplasm and 
(2) a non-nucleated pigmented portion. The former becomes a red 
blood-corpuscle, the latter comes to nothing. 
In embryos three days old elements are seen like lymph-corpuscles, 
or like metrocyte nuclei with degenerated cytoplasm. It seems as if 
the nucleated half of the metrocyte of the second generation might 
either increase in haemoglobin and become a red corpuscle, or lose its 
haemoglobin, divide directly, and form white blood-corpuscles. The 
eosinophilous cells have nothing to do with metrocytes, and do not 
occur in the blood until after the formation of blood-forming organs, 
i. e. about the fifth day. 
Growth in Length of the Frog Embryo.^ — Mr. R. Assheton believes 
that in the Frog, as in the Rabbit, there is evidence to show that the 
embryo is derived from two definite centres of growth — the first, and 
phylogenetically the oldest, is a protoplasmic activity which gives rise 
to the anterior end of the body (= gastrula stage). The second gives 
* Archiv f. Mikr. Anat., xliv. (1894) pp. 237-48 (1 pi.). 
t Quart. Journ. Micr. Sci., xxxvii. (1894) pp. 223-43 (2 pis.). 
