VOL. LXXXVII.] PHILOSOPHICAL TRANSACTIONS. l«2g 



seen in this ovum, which increasing daily in its bulk, progressively manifests the 

 formation of the foetus. 



It is a little remarkable that in the rabbit, where the term of utero-gestation 

 does not exceed 30 days, a 3d part of that time should be required to make that 

 opaque spot obvious to the sight, while the remaining -§-ds should suffice to com- 

 plete the formation of the foetus. It appears as if it required a more elaborate 

 exertion of the formative powers of these parts, to produce what might figuratively 

 be called the nucleus of a foetus, than to go on and complete the work. But this 

 remark applies only to the rabbit ; for in the human female, abortions at the 3d 

 month clearly prove that the evolution of the foetus has been perfected some time 

 before. Such an obvious difference cannot fail to impress our minds with doubts 

 and distrust, whenever we are drawing inferences from analogical reasonings : but 

 to trace the formative process of nature through this work, and to compare her 

 progressive advances in the different periods of utero-gestation, are foreign to the 

 design of this essay. 



IX. Experiments in which, on the Third Day after Impregnation, the Ova of 

 Rabbits were found in the Fallopian Tubes ; and on the Fourth Day after Im- 

 pregnation in the Uterus itself '; with the first appearances of the Foetus. By 

 Wm. Cruikshank, Esq. p. 197. 



The ancients imagined that the woman had her testicles, as well as the man, and 

 her own semen. They taught, that in the coitus there was a mixture of the male 

 and female semen in the uterus, and that from a process like fermentation between 

 these 2 fluids, an embryo was produced. Lewenhoeck said the embryo belonged 

 to the male ; and saw, or thought he saw, animalcules in the male semen, resem- 

 bling the animals to which they belonged. Spallanzani says, that the semen of 

 male animals having no animalcules, impregnates as certainly as that of those which 

 have them. This shows that those animalcules are not embryos. Steno, observ- 

 ing that there were round vesicles in the testicles of women, like the eggs of birds, 

 called them ovaria, and said their structure was exactly similar to the ovaria of 

 birds. After this the immortal Harvey broached the doctrine of " omnia ab ovo ;" 

 that all animals were produced from ova. " Nos autem asserimus, animalia omnia, 

 et hominem ipsum, ex quibusdam ovis nasci." 



The ova in the ovaria of rabbits are particularly described by De Graaf, whence 

 Haller calls them ova Graffiana. But the ovaria of quadrupeds often contain vesi- 

 cles of the hydatid kind ; and it becomes difficult to distinguish between what are 

 vesicles, and what are ova. The mark with me is this : the ova are inclosed in a 

 capsule highly vascular from arteries and veins, carrying red blood. The hydatid 

 vesicles are not vascular ; at least their vessels carry no red blood. The calyx and 

 the ovum, after impregnation, and even before it, in the state in which the qua- 

 druped is said to be hot, become black as ink, from the greater derivation of blood ; 

 and the ova resemble dark spots : they also come nearer the surface of the ovarium, 



VOL. XVIII. S 



