April*), 1885] 



NA TURE 



535 



their eggs after deposition, I have selected this subject 

 for the introductory lecture, since some opportunities have 

 lately been afforded for its investigation in our own 

 waters. These facilities have occurred at sea in con- 

 nection with the Trawling Commission, and on land 

 at the Marine Laboratory — now, I am glad to say, 

 established, by the aid of the Scotch Fishery Board, 

 within easy reach of the students of Natural History in 

 this University. 



The subject, moreover, is one of general interest, for it 

 is but a short time since works devoted to the history of 

 British fishes were devoid of allusion to any other mode 

 of spawning than that by which the eggs of our marine 

 fishes were deposited on the bottom of the sea. Indeed, 

 it was believed by most naturalists that the latter was the 

 normal mode of deposition. As a consequence, some of 

 the text-books at present in use either follow the latter 

 view, or do not specially allude to the question. Under 

 these circumstances, it is not surprising that the majority 

 of those who have spent their lives from boyhood onward 

 at the pursuit of line-fishing should maintain, even at this 

 moment, that the eggs of all marine fishes are deposited 

 at the bottom of the sea — with a tenacity all the more 

 persistent as several apparent corroborations by experi- 

 ment which they had, with praiseworthy interest, made, 

 and which I shall allude to by and by) seemed to justify 

 their opinion. 



The eggs of all fishes are produced in the ovaries — 

 symmetrica] organs which lie beneath the vertebral 

 column, and which at different periods of the year present 

 various appearances according to the degree of develop- 

 ment of the eggs. Thus in the quiescent condition of the 

 organs, as in the case of the green cod before you, their 

 size is insignificant, while the fully-developed ovaries 

 occupy a large space and weigh several pounds. At first 

 the eggs are very small, but they gradually increase in 

 size by imbibing nourishment from the ovarian follicles in 

 which they are placed. 



A feature not sufficiently insisted on in our country is 

 the fact that only a portion of the ovary in most marine 

 fishes becomes " ripe " at a given time, the matured eggs 

 passing along the oviduct and escaping externally. This 

 provision appears to be admirably suited for the increase 

 of the fishes, a constant succession of embryos being thus 

 liberated, and time afforded for those of one stage to dis- 

 appear, as we shall afterwards see, from the surface of the 

 ocean before those of the succeeding take their places. 

 In America this condition has been clearly described in 

 the Report on the cod-fisheries of Cape Ann, by Mr. 

 Earll, for the United States Fish Commission in 1880 ; 

 but the account does not seem to have come under the 

 notice of Mr. Oldham Chambers, who alluded to the 

 subject a year or two afterwards. 1 Mr. Earll observes 

 that the individuals {i.e. the cod) do not deposit all their 

 eggs in a single day or week, but probably continue the 

 operation of spawning oxer fully two months. The result 

 of this arrangement is that the American cod begin to 

 spawn in September, and some continue as late as June. 

 The cod in our own seas do not follow the same habit, 

 though their spawning-period extends on each side of the 

 beginning of April. In the same way the period during 

 which the eggs of the various kinds of skate are deposited 

 is considerably lengthened. 



On the other hand, such marine fishes as the lump- 

 sucker and bimaculated sucker, the salmon, trout, and 

 most freshwater fishes seem to deposit their eggs within 

 the limited period of a day or two, and consequently the 

 development of the masses of eggs in the ovaries is more 

 nearly simultaneous. 



The importance of this point in the history of the eggs 

 of fishes will be apparent when it is viewed in connection 

 with a close time in legislation ; for while nothing could 



1 " Fish rind Fishes," Prize Essay?, International Fisheries Exhibition, 

 Edinburgh. 1833. p. 187. 



be more simple than the fixing of such a period in the 

 case of the salmon, which spawns in rivers, it would be 

 very different in the case of such as the cod, sole, and 

 turbot, both on account of the lengthened and diverse 

 periods in each case, and the vastness of the field in 

 which it is to be applied. 



In general form the eggs of ordinary fishes are circular. 

 On deposition they are usually invested by a single layer 

 (zona radiata), though in some, as in the herring, there is 

 another, viz. the vitelline membrane, which lies outside 

 the former. The great mass of the egg is formed by the 

 oval spherules of the food-yolk, which are separated by 

 protoplasmic bands. Near one of the poles the proto- 

 plasm usually forms a lenticular area, the germinal disk 

 or germinal area, and the smaller yolk-spherules in this 

 region differ in character from those of the general mass 

 of the egg. During development the eggs show partial 

 segmentation, this process being chiefly confined to the 

 germinal area. 



While the circular form as just described is charac- 

 teristic of the eggs of most fishes, we have a few marine 

 types which deviate from the general rule, e.g. Myxine 

 (glutinous hag), with its ovoid and fringed eggs, the 

 goby, with its fusiform ova, the gar-pike, saury pike 

 and flying-fish, which have long filaments attached to 

 their eggs — probably for the purpose of fixing them to 

 floating structures of any kind. Amongst other interesting 

 types are the large eggs of the stickleback and the salmon- 

 tribe, and the almost microscopic eggs of the eel. The 

 large ova of the salmon and trout are surpassed, however, 

 by those of the Siluroid genus Arius — found both in the 

 Old World and the New (Ceylon and Guiana) — the eggs 

 being somewhat larger than a pea (5- 10 mm.) : but this is 

 not the only remarkable feature in these fishes, for, as 

 Drs. Giinther and Wyman and Prof. Turner have shown, 

 the large eggs are carried by the male in his mouth and 

 gill-chamber until hatched, the small and almost granular 

 palatine teeth making this possible, without injury to the 

 ova. He thus acts the part of a dry nurse, as also does 

 the male pipe-fish [Sy/iguathus), and the sea-horse {Hippo- 

 campus), the eggs being borne by the male in a pouch on 

 the under surface. In another Siluroid fish (AspreJo) 

 from Guiana the remarkable exception occurs of a female 

 rish interesting itself in the care of its young. The skin 

 on the under surface becomes soft and spongy, and the 

 eggs, which are deposited on the ground, adhere by 

 simple pressure of the body over them — very much after 

 the arrangement in the Surinam toad. Only one other 

 female fish shares with this one the distinction just noted, 

 viz. Solenostoma, an Indian Lophobranch, in which the 

 ventral fins (free in the male) coalesce to form with the 

 integuments a pouch for the reception and hatching of the 

 eggs. The entire group of the sharks and rays (Elas- 

 mobranchs), again, is characterised by the peculiar con- 

 dition of their eggs, which are not only distinguished by 

 their great size, but by the fact that they are either de- 

 posited in horny capsules, or retained in the oviduct until 

 hatched. The former takes place in the common rays, 

 certain dog-fishes {Scyllium), and sharks (Cestraciori), 

 and in the curious Chimara and Callorhynchus j while 

 the latter, that is the production of living young, occurs 

 in the rest of the sharks and in Torpedo. 



As already indicated, the prevalent notion amongst the 

 older naturalists was that fishes of all kinds deposited 

 their eggs on the bottom of the sea, and that extensive 

 migrations were made by various kinds for this purpose, 

 the general impression being that the majority proceeded 

 shorewards to deposit their eggs in the shallow water. 

 'Hi, 5 impression was probably due to the fact that the 

 salmon, and perhaps the herring, followed this habit, the 

 former proceeding up rivers, and the latter selecting 

 certain suitable banks (often near land) covered with sea- 

 weeds and zoophytes, or a bottom composed of stones 

 ami -ravel. Building their notions on these facts, it was 



