86 MR. HOGG ON THE MODES OF 



The author next notices the structure of the male and female 

 organs of the Salmonidce " as seeming to render impregnation 

 from without very improbable." 



He continues (p. 4) — " That the fish, in the act of spawning, 

 sometimes come in contact, pressing against each other, and 

 thereby aiding the expulsion of the ova and milt, cannot, I think, 

 be doubted. By many observant fishermen-poachers, addicted to 

 the taking of the fish at the time of their spawning, I have been 

 assured of the fact from their own observations. But this is very 

 different from the act of copulation, as performed in other classes 

 of animals, in which impregnation is effected before the expulsion 

 of the ova ; but though so dissimilar, perfectly suitable to the 

 end required, and quite in accordance, as we have proof in the 

 artificial process, with the necessary requirements." 



Dr. Davy concludes thus: — "Granting the observations re- 

 ferred to — of the hatching of the ova of the Trout in the manner 

 described — ^viz., without milt, so far as was known, being brought 

 into contact with the expressed ova — to be accurate in their 

 detail, it may be asked, Does the result, as stated, warrant the 

 inference, that impregnation was effected before the expulsion of 

 the ova ? The box, we are informed, containing them was placed 

 in a stream. What is more likely than that they might have 

 been impregnated, so included but not insulated, by the spermatic 

 granules, the spermatozoa of milt shed by some fish in the adjoin- 

 ing water ? The diffusibility of these living granules (animalcules^ 

 J. H.) — not the least remarkable of their qualities — seems to be 

 favourable to this conclusion." 



Further, Dr. John Davy, in his little book, " The Angler and 

 his Friend," only published last year, and which I have before 

 cited, again relates the same account of Dr. Robertson's ex- 

 periment, as reported in the " Perth Courier," and other papers, 

 in the following dialogue: — 



Amicus observes (at page 141), " I have recently read in more 

 than one provincial newspaper, that the ova are impregnated not 

 after, as you say, but before their exclusion, and consequently 

 that the mixing of the roe and milt in the artificial process, as it 

 has been called, of breeding Salmon, is unnecessary." 



