ON GENERATION. 233 



clear diffluent fluid, whether I should regard it as the innate 

 heat, or radical moisture ; as a matter prepared for the future 

 foetus, or a perfectly-concocted nourishment, such as dew is 

 held to be among the secondary humours. For it is certain, 

 as shall be afterwards shown, that the earliest rudiments of the 

 foetus are cast in its middle, that from this the chick derives 

 its first nutriment, and even when of larger size continues to 

 live amidst it. 



This solution therefore increases rapidly in quantity, par- 

 ticularly in its internal region, which, as it expands, forces out 

 and obliterates the external regions. This change is effected 

 in the course of a single day, as is shown in the second figure 

 of Fabricius. It is very much as it is with the eyes of those 

 animals which have a very ample pupil, and see better by night 

 than by day, such as owls, cats, and others, whose pupils expand 

 very much in the dusk and dark, and, on the contrary, contract 

 excessively in a brilliant light : one of these animals being taken 

 quickly from a light into a shady place, the pupil is seen to 

 enlarge in such wise that the coloured ring, called the iris, is 

 very much diminished in size, and indeed almost entirely dis- 

 appears. 



Parisanus, falling upon these regions, is grossly mistaken 

 when he speaks of " a honey-coloured, a white, a gray, and an- 

 other white circle ;" and says that " the foetus is formed from 

 the white middle point " (which, indeed, appears in these 

 regions), and that " this is the semen of the cock." That he 

 may exalt himself on a more notable subtlety he continues : 

 " Before any redness is apparent in the body of the foetus, two 

 minute vesicles present themselves in it; in the beginning, 

 however, neither of them is tinged with red ;" one of these he 

 would have us receive as the heart, the other as the liver. But 

 in truth there is neither any vesicle present sooner than the 

 redness of the blood is disclosed; nor does the embryo ever sud- 

 denly become red in the course of the first days of its existence; 

 nor yet does any of these vesicles present us with a trace of the 

 liver. Both of them belong, in fact, to the heart, prefiguring 

 its ventricles and auricles, and palpitating, as we shall after- 

 wards show, they respond reciprocally by their systoles and 

 diastoles. 



