Fishes. 2543 



the captain, who, however, — and it redounds greatly to his skill and ability as a 

 seaman, when we take into account that the space traversed without this important 

 adjunct to navigation was 2,700 miles of latitude — succeeded in bringing his vessel 

 safely into port in the unprecedentedly short space of 101 days from London. — Sun 

 Newspaper, July 9, 1 849. 



Abstract of a Paper, by John Quekett, Esq., " On the Structure and Mode of Growth 

 of certain of the Tissues and Organs of the Trout (Salmo fario) after its exclusion 

 from the Egg* 



The author commenced by describing in detail the different processes in the deve- 

 lopment of Fishes generally, which, according to Professor Owen, are six in 

 number, viz. — 1. Semination, or the development of the impregnating corpuscles 

 called seminal animalcules or spermatozoa. 2. Germination, or the development of 

 the germ or ovum, susceptible of impregnation. 3. Fecundation, or the act of impreg- 

 nation. 4. Toetation, or development of the embryo within the ovum. 5. Exclusion, 

 or expulsion of the generative product from the parent. 6. Growth, or development 

 from the period of exclusion, or of extrication from a previously excluded ovum to 

 maturity. 



The author then stated that the last process was the only one to which attention 

 would be particularly directed in the present communication. 



Immediately after the ova have been brought into contact with the fertilizing fluid 

 of the male, a series of changes commence ; these, which have been investigated with 

 great care by Vogt, in a species of Salmon, termed Coregonus, and by other conti- 

 nental physiologists in fishes of various kinds, may be described as follows. The first 

 change that takes place is a separation of the chorion or outer membrane from that of 

 the yolk or membrana vitelli. The germinal vesicle then becomes opaque, increases 

 in size, and swells up beneath the membrana vitelli ; the small granules diffused 

 through the yolk become collected at the base of the swelling ; a very short time after 

 this the swollen part divides into two, which in the space of a quarter of an hour, are 

 subdivided into four, then into eight, sixteen, and so on, until at the end of three or four 

 hours the subdivisions are so small, as hardly to be perceptible, the yolk at this time 

 presenting again a smooth appearance. The next stage to be observed, according to 

 Professor Owen, is a slight separation of the yolk into two unequal parts, in the smaller 

 of which two parallel ridges appear, termed the lamina dorsales ; these soon unite and 

 form the nervous axis, and the chorda dorsalis, the smaller portion of the yolk then 

 splits into two layers, an outer and an inner; from the first are developed the brain, 

 vertebra?, muscles, nerves and skin, and from the inner, the organs of digestion, circu- 

 lation, respiration, &c. After the trunk is developed, the head and tail appear, the 

 embryo then encircles the remaining yolk, and at this time its movements are percep- 

 tible. Whilst these changes are taking place in the external figure of the little 

 embryo fish, the blood vessels, nerves, and vertebral column are being developed in 



* Read before the Microscopical Society of London, June 20, 1849. (See Zool. 2506.) 



