708 SUMMARY OF CURRENT RESEARCHES RELATING TO 



deposited, which probably consists only of membrana clastica interna, 

 though a membrana Umitans externa may sometimes bo present. The 

 pectoral fins appear early, as a fold of epiblast into which mesoblast 

 protrudes. 



The paper concludes with certain diagnostic features and details, 

 by which the ova of various food-fishes can be distinguished — such 

 as size, shape, character of capsule, &c. In the embryos the pig- 

 mentation lias some diagnostic value ; the most favourable conditions 

 for hatching the eggs, such as temperature, the chemical purity of the 

 water, and so on, are given. The author draws this conclusion from 

 his study of the development of fishes, " that the Telcostci cmbryo- 

 logically, as also morphologically, arc a highly sjwcializDd group, 

 and arc too far removed from the primitive or protichthyoid type to 

 yield much material for broad generalizations." Though Teleostoan 

 embryology has not the interest possessed by Selachian development, 

 it is nevertheless of very great practical importance. 



Biology of the Trout.* — Dr. D. Barfnrth has investigated some 

 of the reproductive relations of the trout, especially in regard to 

 sterility and degeneration. 



The di rility of the trout is temporary. — By careful observation 

 he has been able to demonstrate that the majority of sterile specimens 

 become mature by the next spawning-time, though some forms require 

 at least two years to become ripe for spawning. The sterility, though 

 temporary, may extend over two spawning periods. 



The most important cause of this temporary sterility is the pre- 

 vention of spawning. When the ripe elements are not liberated, 

 for various reasons, e.g. Avant of suitable depositing ground, un- 

 favourable temperature, nutrition, &c, degeneration and rcabsorption 

 set in with the result that hypertrophied organs become sterile. If 

 the reproductive products are retained for several spawning periods 

 successively, the organs begin to exhibit a connective-tissue degener- 

 ation, and a permanent sterility may ensue. The absorption of the 

 unexpelled reproductive elements is preceded by simple dissolution, or 

 by fatty and mucous degeneration. The white blood-corpuscles do 

 not seem to play any, or at least no important part in the absorption ; 

 their appearance is merely a secondary accompaniment. 



The degeneration of the elements is next described in detail. 

 Even in normal conditions a follicular degeneration occurs in the 

 ovary of the trout. The granulosa cells proliferate and perhaps 

 enlarge, while the yolk exhibits fatty degeneration. The formation 

 of new reproductive elements is affected by the necessary absorption 

 of older unexpelled eggs and sperms, and advances in proportion to 

 the progress of the latter process. The evil influence of the hindered 

 spawning is not confined to modifying the ovary, for it has been 

 proved further that the mature elements afterwards produced result 

 in degenerate organisms ; the fertilized ova of such pond-trout pro- 

 duced relatively weak forms. The value of the research is increased 

 by a wide survey of relative literature. 



* Arch. f. INTikr. Anal, xxvii. (1S8G) pp. 128-78 (2 pis.). 



