THE STOCKING OF THE CLYDE WITH GREYLING. 251 



that of the perfect fish being observed daily with a micro- 

 scope : 



" ' 4:th day. They seem a little larger, and consist of 

 an outer vesicle of elastic membrane, filled with a semi- 

 transparent fluid, and of an inner vesicle or yolk filled 

 with a yellow granular substance, and on the inner vesicle 

 is a spot indicating the germ of the future fish. 



" ' 6th day. The form is slightly altered. The fluid 

 appears flocculent. 



" ' 8th day. The live foetus is visible. It is of a semi- 

 transparent yellow-amber colour j the head in three lobes. 

 The fish lashes its tail violently at regular intervals, eight 

 or ten times a minute. The granules partially absorbed. 



" ' Wth day. Temperature of the room, 55 ; river 

 (Derwent), 52. Foetus less active. 



" ' 30th day. The foetus made its first partial detach- 

 ment from the enveloping membrane by freeing its tail. 

 About half-an-hour afterwards it entirely and suddenly 

 disconnected itself from the chorion, which sank to the 

 bottom of the glass. Temperature, 60. The eyes well 

 developed, the mouth seems still closed. The umbilical 

 sac filled with granular matter attached to the thorax. 

 Pulsation regular. Above the place of the hinder part of 

 the gill-cover a constant and rapid motion is apparent, 

 above 160 per minute. This may be from the vibrating 

 edge of a fine membrane, which at present forms a sub- 

 stitute for the true gills, or it may be from the rapid cir- 

 culation of the blood in loops coming to the water to be 

 crated, or it may be from cilia on the edge of the mem- 

 brane. The membrane, or whatever looks like it, is so 



