Royal Society. 493 



form four series of salts ; •which, in the case of oxide of lead, consist 

 of equivalents of resin and of oxide in the proportions, respectively, 

 of two to one ; three to two ; one to one ; and one to two. This 

 soluble resin in combining with bases does not part with any of its 

 oxygen ; but if any change takes place in its constitution, it consists 

 in the hydrogen being replaced by an equivalent proportion of a 

 metal ; and formulae are given representing the salts of lead on this 

 theoretical view. By boiling the resin in contact with ammonia and 

 nitrate of silver, or perhajis Avitli nitrate of ammonia, it is converted 

 into a resin which forms a bisalt with oxide of silver, in which there 

 is also an apparent replacement of hydrogen by silver. 



The resin next examined is that of dragon's blood : and the con- 

 clusions deduced from its analysis are the following. First, that the 

 lump dragon's blood is the natural and pure resin, while the strained 

 and red varieties, being manufactured articles, are more or less de- 

 composed : secondly, that this resin retains alcohol and ether, as 

 most other resins do, with considerable tenacity ; but that these sol- 

 vents may be entirely expelled by a long-continued exposure to a 

 temperature not higher than 200° Fahr. : and lastly, the formulee 

 representing its chemical composition is given. 



"Researches in Embryology." — Second Series. By Martin 

 Barry, M.D., F.R.S.E., Fellow of the Royal College of Physicians 

 in Edinburgh. Communicated by P. M. Roget, M.D. Sec. R.S.* 



The author having, in the first series of these researches, investi- 

 gated the formation of the mammiferous ovum, describes in this 

 second series its incipient developement. The knowledge at present 

 supposed to be possessed of the early stages in the developement of 

 that ovum, consists chiefly of inferences from observations made on 

 the ovum of the bird. 



But there exists a period in the history of the ovum of the mam- 

 mal, regarding which we have hitherto scarcely any direct or posi- 

 tive knowledge. It appeared, therefore, highly desirable to obtain 

 a series of observations in continuous succession on the earliest stages 

 of developement. In conducting this investigation, the author pur- 

 posely confined his attention to a single species, namely, the rabbit, 

 of which lie examined more than a hundred individual animals. 

 Besides ova met with in the ovary, apparently impregnated, and 

 destined to be discharged from that organ, he has seen upwards of 

 three hundred ova in the Fallopian tube and uterus ; very few of the 

 latter exceeding half a line in their diameter. The results of these 

 investigations have compelled the author to express liis dissent from 

 some of the leading doctrines of embryology, which at present prevail, 

 as respects not only the class Mammalia, liut the animal kingdom at 

 large. The following are the principal facts which tlie author has 

 observed in the develojjcment of the inammifcrous ovum. 



The difference between the mature and immature ovum consists 

 in the condition of the yelk ; the yelk of the mature ovum contain- 

 ing no oil-like globules. Both maceration and incipient absorption 



* An abstract of Dr. Barry's First Series of Researches in Embryology 

 will be fouiul in L, & E. I'hil. Mag., vol. xiii. p. 458. 



