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SUMMARY OF CURRENT RESEARCHES RELATING TO 
stomial canal connecting it with the body-cavity are detached portions of 
the coelom, the equivalents of which are not so differentiated in the 
pronephros. This last is developed as a larval excretory organ, and it is 
suggested that the period at which it appears largely accounts for its 
peculiarities of structure. 
So far as the excretory organs may throw light on the origin of the 
Vertebrata, Mr. Field is of opinion that the group of animals which 
presents nephridia most closely resembling those of Vertebrates is 
unquestionably that of the Cliaetopod Annelids, while the Vertebrate 
excretory system can be readily derived from that of Annelids by a 
series of steps which are in accord with the evidence afforded by the 
ontogeny of Vertebrates. At the same time he is careful to point out 
that none of the evidence is final, for we have no means of saying defi- 
nitely what part has been played by physiologically similar needs in 
moulding the structure of the organs. 
The author details and discusses the views of the numerous writers 
who have, especially in recent years, made contributions to this subject. 
Breeding and Embryology of Frogs.* — Dr. J. H. Morgan states that 
the series of diagrams of the segmentation of the ovum ordinarily found 
in text-books is exceedingly diagrammatic and gives an entirely 
erroneous impression as to the appearance of the segmenting egg, 
especially during the later stages. Ruuber has given excellent figures of 
the later stages of frog’s eggs, and Dr. Morgan has in many points verified 
his account. Up to the eight-celled stage the segmentation is very 
regular, but after that no particular planes of division can be prophesied 
for any segment. 
Newport’s experiments on the orientation of the egg are the most to 
be relied on, and the author has been able to verify his results on a small 
scale. 
Development of Engystoma.t — Mr. J. A. Ryder has some notes on 
the development of the “ frog- toad,” as it is called by the natives of 
North Carolina. The larvae escape from the envelope three days after 
the deposition of the ova. Through the whole course of development 
there is well-marked evidence of the action of gravity in maintaining 
the equilibrium of the egg, the heavier or light-coloured vegetative pole 
remaining lowermost. There seems to be no tendency to rotate the egg 
through ciliary action, previous to the closure of the medullary folds. 
The fact that no change of position occurs for a long time in the eggs of 
Engy stoma would indicate that possibly the future cephalic pole of the 
egg bears a constant relation to the cephalic pole of the parent, such as 
is known to be the case in Batrachus tau. As such relations between 
parent and offspring exist to a marked degree, if they are not universal 
in plants, Mr. Ryder justly remarks that it is desirable to know to what 
extent this rule holds for animals. 
As soon as the larvae become free they swim about actively ; not, 
however, like a fish, for they revolve on their own long axes ; after a 
day they take to the usual fish-like mode of progression. The adhesive 
organs of the mouth soon become functional ; the head begins to widen 
Amer. Natural., xxv. (1891) pp. 753-60. 
f Tom. cit., pp. 838-40. 
