20 Fishery Board for ScMland. 



Bay on 1st August 1901, in 6 to 12 fathoms, contained eggs with embryos far 

 advanced in development, and indeed some of the embryos had already hatched 

 out. 



While positive evidence as to the buoyancy of the sheets of spawn is as yet 

 perhaps too meagre, a study of the remarkable adaptations of the larval and post- 

 larval forms to a pelagic life will convince one that the method of oviposition is 

 admirably adapted to a long period of flotation for the eggs, if not at the surface 

 for the whole period, at least in the upper and middle water layers. 



The eggs are spread out in a single layer and bound loosely together, in a 

 gelatinous matrix, which is often over 30 feet long, 2 feet broad, and less than 

 3 mm. thick. This thin sheet of spawn may, therefore, cover an area of over 60 

 to 70 feet square. It is well known that such a body in which the surface is not 

 only large compared with its volume, but whose surface presents a large area at 

 right angles to the direction of sinking, will sink much more slowly than a body of 

 a similar volume but with a much smaller surface. High specific gravity and 

 viscosity of the water are also factors which will aid the flotation of the spawn over 

 an extended period. 



There is no very definite information regarding the length of time which the 

 eggs of the Angler take to hatch. The statements made by Fulton (1902) may be 

 conveniently quoted here : " The nature of the yolk, and the advanced condition 

 of the larva on issuing, argue a more prolonged period for the embryonic development 

 than in the case of pelagic eggs. On the other hand, the temperature of the surface 

 water in May, and still more in June and July, is high, and, judging from the period 

 in the case of a large pelagic egg like that of the plaice, it is probable that the eggs 

 of the Angler require over three weeks in May and njore than a fortnight in July 

 before hatching occurs." 



As already stated, the larvae hatched from isolated eggs retained considerable 

 yolk even after they had been hatched a week. They also floated at the surface 

 of the water. In the sheets of spawn, however, the newly-hatched larva does not 

 immediately escape from the investing gelatinous sheet. Agassiz' illustration 

 supports this conclusion. Fulton, describing the sheet of spawn obtained by him 

 in Aberdeen Bay, states that the embryos were well advanced, and that some had 

 already hatched out. 



Thus, the specific gravity of the eggs themselves and the loose binding together 

 in a gelatinous matrix of extended surface, tend to ensure for such large eggs flotation 

 in the upper water layers and for the larva, with yolk much reduced and pectoral 

 fins well developed, liberation from the investing jelly as far as possible from the 

 bottom. 



A consideration of the remarkable developmental changes which take place 

 during pelagic life will at once convince one that the transitions are gradual, and 

 that the typical bottom form is attained only after an extended period. 



Large surfaces, at right angles to the direction of sinking, are develoj)ed by the 

 extraordinary increase in length and in spread of the membranous pelvic fins. 

 These long and greatly expanded fins, inserted very far forward on the ventral 

 surface of the body, add greatly to the surface without a corresponding increase 

 in weight, and hence by the lively up-and-down motion of these membranous 

 planes, the small forms will not only keep suspended in the water, but will tend to 

 rise to the upper water layers. 



Stiasny's statements regarding the mode of life of the older post-larval forms 

 are instructive. These were caught in the Bay of Trieste, in the day-time, but not 

 in the open sea. He caught them with a simple hand-net, or with a small net on 

 a long rod. " They are lively swimmers, while the adults are ground dwellers. 

 We usually found them swimming in the upper water layers or in small depths in 

 which they were easily seen by their thread-like appendages, and the Uvely up- 

 and-down motion of their pelvic fins in striking contrast to the strongly vibrating 

 pectoral fins. Sometimes we found them suspended without motion in the water 

 or on the rocky wall of the harbour, lying peacefully upon the rich and luxuriant 

 sea-weed." 



There are other modifications for a pelagic existence in these small forms. 

 The embryonic fin, at the escape of the larva from the egg is very broad, and it 

 persists for a remarkably long period. It even persists after 'the true fins have 



