of the Fishery Board for Scotland. 



81 



Preservation of Tow- Net Collections. 



Each collection was preserved in formalin. Commercial formalin 

 was reduced with sea-water (39 parts sea-water to 1 part formalin) until 

 the mixture contained 1 per cent, of formic aldehyde. This fluid 

 preserved the eggs very satisfactorily, there being no immediate 

 shrinkage. After 12 months' immersion in the fluid the shrinkage was 

 about 3 "5 per cent. The eggs moreover remained very translucent. 

 Fish larvae, however, were not preserved well, unless separated from the 

 rest of the tow-net collection. The liquid was changed once or twice, 

 and a large quantity of fluid (proportionally) given the material to be 

 preserved. 



Method of Treatment of Results. 



The results will be discussed in the following order : — 



1. An enumeration of the species the eggs of which were found in 

 Loch Fyne. 



2. A discussion of the times of occurrence and relative abundance of 

 the eggs of different species. 



3. The stages of development of the eggs. 



4. A comparison between the different stations as to the abundance of 

 pelagic ova and Copepoda. 



5. The estimated numbers of the eggs of different species in Upper 

 Loch Fyne. 



6. The discussion as to the depth at which pelagic eggs and copepods 

 float. 



7. On the drift of eggs, &c. 



8. List of young fishes captured in the tow-nets. 



The Identification of the Ova. 



While the identification of some of the ova, either in the fresh or 

 preserved condition, is doubtful, there are certain species which, by the 

 possession of oil globules, markings on the zona, etc., are very readily 

 diagnosed. The egg of the plaice is by its large size separated sharply 

 from all other pelagic eggs. An accurate determination of the numbers 

 of the eggs of every species of the Gadoids is so far not possible. The 

 variation in the size of the eggs of a species introduces a difficulty which, 

 until a determination of the percentage number that vary on either side 

 of the average size is made, prevents an accurate separation of each 

 species. It is always possible by means of size to diagnose the majority 

 of the eggs of a species. Thus, for example, in the case of the eggs of 

 cod and haddock, in the preserved condition, the average size of the 

 former is 1*32 — l*34mm. diameter, while of the latter 1*41 is the average 

 size. In a mixture of cod and haddock eggs, then, the method which has 

 been followed has been to separate the two by the size l*39mm. Eggs 

 of greater diameter— viz., from 1'39 — l*5mm. diameter — have heen 

 regarded as those of haddock; while those eggs measuring 1*3 — l*39mm. 

 have been diagnosed as those of cod. It is among the eggs of 

 the cod and haddock that the greatest difficulty exists in this 

 respect, but from a very careful tabulation, and by the construction of 

 a curve, of the sizes of the eggs of these species collected in March 

 — 2277 in number — the great majority can be separated. For the other 

 Gadoids present the average size for each is as follows : — Whiting, 1 "2mm. ; 

 saithe, l"13mm. ; bib, l-07mm. ; poor-cod, -93mm.; pollack, l'llmm. 



