308 Linnaan Society : — 



time and artificially impregnated. They were taken by Mr, Harrison 

 in December last, and sent to Mr. Hogg in January by Isaac Fisher, 

 Esq. of Richmond, Yorkshire. " The ova in both phials," says Mr. 

 Harrison, " were taken from one fish in the River Tees, on the 27th 

 of Dec. 18o3. The female fish was held up by the head, and when 

 the spawn was ready it run out by itself. The ova were with the 

 milt for about half a minute, or as soon as they could be got away. 

 The impregnation naturally takes place in a moment, as is always 

 the case in a stream, where the milt shed in the running water 

 passes rapidly over the ova." Mr. Hogg was unable to obtain either 

 the immature ova fi-om the same female, or ova naturally fecundated 

 — two other conditions which he was desirous of examining to com- 

 plete the series of his observations. 



The object which Mr. Hogg had chiefly in view was the micro- 

 scopic examination of the external membrane of the ovum in these 

 several conditions, in relation to the statements made by different 

 authors as to its structure and the changes it is supposed to undergo. 

 Thus in the ' Book of the Salmon,' by Messrs. Fitzgib])on and A, 

 Young (Lond. 1850), it is stated (p. 183), that " the eggs of that part 

 of the roe nearest to the vent will be always found of larger size than 

 those situated higher up in the stomach ; they are softer also, and 

 their outward filaments (or membranes) are thinner and more porous, 

 and thus they are fitter for impregnation — for absorbing the milt of 

 the male as it is poured over them." An'& again, p. 185, " Although 

 the unripe ova should be expressed, they would be useless for pro- 

 duction, for their absorbing pores are still closed against the inter- 

 penetration of the milt, and consequently in this state impregnation 

 is impossible." In like manner Mr. Jacobs, in a communication 

 published in the ' Hanover Magazine' for the year 1763, quoted in 

 Yarrell's ' British Fishes ' (ed. 2nd, vol. ii. p. 93), says of the common 

 Trout and of the Salmon also, " After an egg has been fructuated by 

 the sperma of the male, which slips through an invisible opening 

 into it, it lodges in the white liquor, under the shell and round the 

 yolk." Recent discoveries, Mr. Hogg continues, have shown that 

 the fecundating principle of the male fish (as of every animal in 

 which there is a sexual communion) is solely derived from the 

 seminal animalcules or spermatozoa. In the words of our late 

 distinguished Fellow, Mr. Newport, " The spermatozoa alone, in all 

 cases of communion of the sexes, are the sole agents in impregnating 

 the ovum, and impregnation cannot be effected by the liquor seminis " 

 (Phil. Trans. 1851, p. 172). Dr. Martin Barrv indeed has asserted 

 (Phil. Trans. 1840, p. 533, and pis. 22 & 23." figs. 164-169) that 

 he had observed an attenuation, or an orifice like a cleft, in the thick 

 transparent membrane of the ovum of the Rabbit, at the period of, 

 and after, fecundation, through which the spermatozoa enter ; and 

 in a recent communication to the Royal Society (Proceedings, vol. vi. 

 p. 335), the same author has referred to a lately published work by 

 Dr. Keber, in which Dr. Barry states, " That physiologist describes 

 the penetration of the spermatozoa into the interior of the ovum, in 

 Unio and Anodonta, through an aperture formed by dehiscence of its 



