The Isolated Egg. 5 



vessels, hitherto no records have been publislied of the occurrence of the egs;s or 

 larvte of Lophius piscatorius. 



Amongst the many collections made by the Goldseeker of pelagic fish eggs 

 of common species, an occasional egg, conspicuous by its large size, and possessing 

 an oil-globule, has appeared from time to time. At first there was considerable 

 uncertainty as to the identification of this species of egg, but on 5th May 1911 

 one was obtained at 59° 26' N. ; 1° 20' W., which gave some clue to its identity. 

 This large egg, separated from the rest of the collection, was kept alive and under 

 observation until the embryo had assumed definite shape within the egg. Un- 

 fortunately, the embryo died before hatching out, but it was sufficiently advanced 

 in development to enable me, from its characters, to decide that the egg belonged 

 to Lophius piiscatorius. The characteristic dendritic, dark, chromatophores had 

 developed over the head of the embryo and over part of the yolk and oil-globule, 

 and this particular specimen also showed the characteristic pigmentation on the 

 gut. All doubts as to the specific identification of these large eggs were cleared 

 away when, in April 1914, similar eggs were obtained, from which the embryos 

 were successfully hatched out and reared until the yolk had been very considerably 

 absorbed. The nature of the egg and the characteristic appearance of the larva 

 are sufficient for the purpose of identification. 



Description of the Isolated Egg. 

 {Fig. 2). 



The isolated egg of Lop)hius is pelagic, large and transparent, with a homo- 

 geneous yolk. The egg, especially in the living condition, is therefore easily 

 distinguished from that of Argentina, in which the yolk is segmented. The pelagic 

 isolated egg of Lophius is enclosed in a very delicate membrane. The perivitelline 

 space is extremely small, even when the embryo is well developed in the egg. It 

 never becomes large. (In eggs which have been kept in preserving fluid for some 

 time, the perivitelline space is sometimes larger, a condition due to the shrinkage 

 of the yolk.) The yolk is usually of a very pale straw or yellow colour, and oil 

 globules like burnished copper or am])er are present on the surface of the yolk. 

 The number of oil-globules varies ; there may be only a single large one, but usually 

 there are one or two larger ones with a variable number of very small ones. These 

 smaller oil-globules may coalesce later, to form a single large oil-globule. 



The eggs are not always perfectly spherical, but often appear more or less 

 oval in shape, with a long and short axis at right angles to each other. 



The following are the measurements of 500 eggs isolated from a mass of spawn 

 caught on 3rd May 1916 at 57° 37' N. ; 0° 53' E. The eggs were measured in the 

 living state, and each egg was measured along its greatest and least diameter — 



Measurements of 600 Eggs caught 57° 37' N.; 0° 53' E.— 3/5/16. 

 50 scale divisions of eye micrometer = 2 mm. 



500 500 1000 



