TRANSACTIONS OF THE SECTIONS. 129 
in the external world, it follows, that if the conditions of existence, 
such as soil, climate, locality, &c. be indefinitely various, the forms of 
animals and plants which are adapted to those conditions must be inde- 
finitely various also. Perfect symmetry would only be compatible with 
the natural system on the supposition that all the variations of the 
earth’s surface, the mountains, rivers, islands, soils, currents and winds 
were absolutely symmetrical in their situations and regular in their 
influences. 
On the Development of the Fish in the Egg. By Professor AGAssiz. 
Professor Agassiz gave an account of his researches on the develop- 
ment of the embryo in the ova of fishes, more especially of the family 
of Salmonide. He detailed at great length the successive changes 
undergone by the various systems of organs. The object he had in 
view in these investigations was to ascertain if there existed any rela- 
tion between the forms of fish of the present day, during the succes- 
sive stages of their development, and the permanent forms of fish 
found in the older strata of the earth. 
On the First Changes consequent on Fecundation in the Mammiferous 
Ovum, with special reference to a Communication “ On the De- 
velopment of the Fish in the Egg,” by Professor Agassiz. By. Dr. 
Martin Barry, F.R.S. 
The remarks were intended as an outline of a memoir, communicated 
by Dr. Barry to the Royal Society of London in March last. The 
memoir itself being now in the course of publication in the Transactions 
of that Society, Dr. Barry stated that he could not, with propriety, 
anticipate its appearance by further details than had been already 
published, as an abstract, in the Society’s “ Proceedings.” He had 
had no intention indeed of offering a paper on the subject to the 
British Association until yesterday, when a communication was made 
by the celebrated naturalist of Neufchatel, which called for some re- 
marks at his hands. 
Nearly every author on the ovum allows the germinal vesicle to be 
its most essential part. The office which this vesicle performs, how- 
ever, and its destination, had been subjects of speculation only. 
Purkinje, the discoverer of this vesicle where it was first found, 
namely, in the bird’s egg, supposed it to burst; and either the same 
opinion, or else that it dissolves, flattens down, or becomes otherwise 
destroyed, had been conjectured by most subsequent observers. All, 
however, including the eminent naturalist whose observations Dr. 
Barry had now more particularly in view, Professor Agassiz, were 
agreed that the germinal vesicle disappears about the period when the 
ovum leaves the ovary. The question is, its mode of disappearance. 
1840. K 
