VOL. LXXXVII.] PHILOSOPHICAL TRANSACTIONS. 127 



investigated this intricate question, I hope with some regularity ; the design of this 

 essay next leads me to consider the state or form of that substance which passes 

 from the ovaries in consequence of impregnation. 



§ 3. What is the Form of that Substance which passes from the Ovaries in conse- 

 quence of Impregnation ? 



No sooner had the researches of the physiologists retraced the existence of the 

 new-born animal to the ovaries, than their curiosity was excited to discover the 

 form it assumed while resident in these bodies, and especially at that particular 

 time when the foetal primordia are about to escape from them. The analogous 

 phenomena of oviparous animals, and the structure of the ovaries as described 

 by De Graaf, concurred to favour an opinion, that in viviparous animals there ex- 

 isted ova in these bodies, and indeed from this very circumstance they received 

 their name. But though several physiologists have concurred in this opinion, there 

 has not been any strict coincidence respecting their state while in the ovary. Some 

 have thought that the vesicles described by De Graaf were the true ova, and that 

 these are the bodies that are expelled by impregnation. Others, with greater pro- 

 bability, have considered these vesicles as the apparatus destined by nature, under 

 the influence of the proper stimulus, to form the ovum : and though at all times 

 they contain a glairy kind of fluid, from the stimulus of impregnation this fluid be- 

 comes a small vesicle or ovum seated within the larger vesicle, which now becom- 

 ing thickened, and acquiring a yellow colour, is called the corpus luteum : from 

 this body the interior vesicle or ovum is protruded. Others again refuse assent to 

 both these opinions, and contend that the substance extruded from the corpora 

 lutea has no vesicular appearance ; and though by some is has been called an ovum, 

 yet that name is not applicable to it from any resemblance of figure, but rather 

 from its agreement with an egg in being the substance in which the rudiments of 

 the future animal are contained. 



De Graaf contended that the primordia of the foetus while in the ovary are vesicular, 

 as appears in his work ; in which, after describing the enlargement of the proper ve- 

 sicles usually connected with his name, he says, " praeterea aliquot post coitum 

 diebus tenuiori substantia praediti sunt, et in sui medio limpidum liquorem mem- 

 brana inclusum continent, quo una cum membrana foras propulso, exigua solum 

 in iis capacitas superest." He is thererefore decidedly of opinion, that as soon as 

 the product of conception becomes the subject of notice, it has a vesicular form, 

 and this he thinks takes place at the end of the 3d day, though the substance passes 

 from the ovaries several hours before this time. He seems rather to assert, that it 

 passes in a vesicular form, than to prove it ; for in 52 hours after the approach of 

 the male, he found the ovarian vesicles were empty, though he could not now rind 

 the new vesicles either in the uterus or the tubes. But in 72 hours they were so 

 evident, that he could distinguish with ease the 2 membranes of which they are 

 formed, viz. the chorion and amnios ; so that they cannot be very small at this 

 time. Hence it would follow, that if on a repetition of this experiment on the 3d 



