[ 431 ] 
XIV. Observations on the Ovum of Osseous Fishes. 
By W. H. Ransom, M.B. Communicated by Dr. Sharpey, Sec. B.S. 
Received June 21, — Read June 21, 1866. 
In November 1854 I had the honour of presenting to the Royal Society a short paper, 
containing the principal results of observations made on the ova of two species of Gas- 
terosteus , and I then expressed an intention of furnishing a more detailed record of them 
at a future time. Since that date my experiments have been continued and extended, 
and I now purpose so to recount them, that physiologists interested in this department 
may be able to judge of the value of the results, and to repeat the observations. 
It is intended in the following pages to consider, first, the unimpregnated ovum, with 
reference to its structure, its physical and chemical properties in the mature state, and 
during its development ; and afterwards the impregnated egg, in reference to the mode 
in which fecundation is effected, the phenomena which follow it, and their modifying 
and essential conditions. 
The Unimpregnated Ovum. 
The Stickleback (Gasterosteus leiurus and G. pungitius). 
1. Bipe deposited ova. — The 3-spined and 10-spined sticklebacks may be taken 
together, as there are no important differences in the structure of their eggs. These 
observations, however, were for the most part made on the former, which are more easily 
obtained in numbers, and where the latter were employed it will be so stated. 
The freshly deposited ova are held together by a colourless, transparent, viscid, mucoid 
matrix ; they are few in number compared with those of many other fishes, and of large 
size, measuring about ff" on the average. To the naked eye they have a pale amber 
tint, and are semitransparent, spherical in form, but irregular, from mutual pressure 
(Plate XV. fig. 1). Each consists of an outer covering, the well-known dotted membrane 
or chorion, which I shall speak of as yelk-sac, understanding that term to mean that 
covering of the yelk which, being formed in the ovary, is placed next in contact with the 
yelk, but takes no part in cleavage ; and a yelk-ball, divisible into formative and food- 
yelk, the former forming a complete cortical layer of granular matter, the latter, the 
chief mass, containing oil in large drops. 
a. The viscid layer is a secretion from the oviduct. It resists for some time the action 
of water and prevents its imbibition in unimpregnated eggs, so that they remain flaccid 
after at least hours immersion. It is then no longer distinguishable as a viscid 
layer, but it makes the eggs cohere firmly together, as if it had the property of setting 
in water. 
3 N 
MDCCCLXVII. 
