On the Relations of the Yolk to the Gastrula in 
Teleosteans, and in other Vertebrate Types. 
By 
J.T. Cunningham, B.A., 
Fellow of University College, Oxford; Superintendent of the Scottish Marine 
Station. 
With Plates I, II, ILI, and IV. 
Tue study of the ova of marine Teleostean fishes is now 
being actively pursued by many naturalists and is yielding 
results which are, in the present stage of the progress of 
zoological science, of great importance. ‘These results are 
of various kinds. Some of them consist in the discovery of 
the conditions which affect the life and development of different 
kinds of ova, and the invention of methods and apparatus by 
which the favorable conditions can be most efficiently pro- 
duced in the biological laboratory or in the premises of the 
pisciculturist. To this class of results the present paper makes 
but little contribution. Another class comprises the descrip- 
tions, measurements, and illustrations which set forth the 
peculiarities characterising the eggs of the several species. The 
knowledge of these peculiarities in the ovum of a given species 
is an addition to the sum of known facts concerning the life- 
history of that species ; and the accurate observation of these 
peculiarities is of special value im the case of pelagic ova, 
because in these inconspicuous features afford the only criteria 
by which the species to which they belong can be ascertained. 
To this second class of results some slight additions are made 
VOL. XXVIL—NEW SER. A 
