14 



Part III. — Sixteenth Annual Ueport 



■ of the sea water in which it is immersed. Hence the general rule 

 ' that pelagic eggs are obtained in the surface layers of the sea, while 

 ' the larvae are found most abundantly towards the bottom and in 



* the middle layers. The expansion of the pelagic ovum at matur- 

 ' ation to three or four times its previous size is also correlated in 



* certain important respects with the life-history of the species. 



* Inasmuch as the entrance of fluid into demersal eggs can have 

 ' no hydrostatic function, it is highly probable that the same change 

 ' is of normal occurrence in many other groups, such as the mam- 

 ' malia, and is associated with the disappearance of the germinal 



* vesicle.' 



In order that the chemical changes which occur in the processes 

 described might be as far as possible elucidated, the Board appointed 

 Dr. T. H. Milroy, of the Physiological Department of the Univer- 

 sity of Edinburgh, to make a research on the subject, and his report 

 is also published in the present volume. It is shown that among 

 pelagic eggs the quantity of water present rises during maturation 

 from about seventy to over ninety per cent, of the total contents, 

 while among demersal eggs it rarely rises over seventy per cent.; 

 and the quantity is constant in the eggs of a particular species. It 

 is also shown that besides the absorption of water there is a con- 

 siderable increase in the salts during maturation ; and a description 

 is given of many hitherto obscure points in the chemistry of the 



Also in connection with this branch of fishery research, Mr. H. 

 Ch. Williamson, M.A., B.Sc, has made a study of the absorption of 

 the yolk, and the primitive circulation in the pelagic eggs of fishes, 

 especially in the haddock, whiting, flounder, hake, anchovy, and 

 muraenoids, in which it is shown that a modified vitelline circu- 

 lation of yolk corpuscle occurs. The respiratory processes in the 

 embryo of teleostean fishes is also described, and illustrated in two 

 plates. 



In another paper Dr. Fulton gives an account, with figures, of 

 the hitherto undescribed ovaries of the angler or monk-fish and the 

 John Dory, together with a description of the ovarian eggs. 



The Post-Lakval Stages of Flat-Fishes. 



In the present Eeport Mr. H. M. Kyle deals with a subject which 

 is frequently of considerable practical importance in fishery 

 questions, namely the identification of fiat-fishes in their very young 

 stages. It is often a matter of much difliculty to identify such 

 young forms living on the beaches or in shallow water, and thus 

 the young of worthless species may be confounded with those of 

 valuable edible forms. Mr. Kyle has made a comparative study of 

 a large number of specimens of the post-larval stages of the plaice, 

 dab, flounder, long rough dab, and lemon sole, and has carefully de- 

 scribed their differential characters and represented them in a 

 scries of figures. 



