[142] 



OVUM. 



quite different from those of Crustacea in 

 their composition, containing albumen, fatty 

 matters, and a large quantity of a substance 

 precipitable by water. 



The ova of Mollusca differ greatly in com- 

 position from those of other animals : more 

 particularly in the entire absence of fat from 

 them. 



From these researches it appears that there 

 are considerable differences in the chemical 

 composition of the ova of animals of different 

 great groups, and even among those not far 

 removed from each other in the zoological 

 scale, and that there are also considerable 

 differences according to the state of advance- 

 ment of the ova of the same animal, more 

 especially it would appear that a marked 

 change of composition takes place at the 

 period of complete maturity. The researches 

 referred to appear to have brought to light 

 several new organic principles which are 

 modifications of albumen or belong to the 

 same class, and which may be considered as 

 Vilcllmc principles as belonging to the yolk 

 of different animals : such are Vitelline, Ich- 

 thine, Ichthidine, Ichthuline, and Emydine. 



The full citations of different works and 

 memoirs on the subjects of this article render 

 it unnecessary to give any detailed bibliogra- 

 phical list at its termination. I may, how- 

 ever, call the attention of the reader to the 

 following works already cited, as forming the 

 principal basis of modern knowledge of ovo- 

 logy and development, viz.: The Inaugural 

 Dissertation of Pander on the Development 

 of the Chick, published in 1817. The His- 

 tory of the Egg before Impregnation, by 

 Purkinje, in 1825. The Epistola of Von 

 Baer, in 1827. The contributions of Von 

 Baer and RatJike to Burdock's Physiology, in 

 1827 and 1828. The various Memoirs by 

 liathke at different times, and Von Baer's 

 Lectures on Development, completed in 

 1837. The Systematic Manual of Develop- 

 ment by G. Valentin, in 1835. The Prodro- 

 mus and contributions by R. Wagner, in 1836. 

 and the Manual of Physiology by the same 

 author. J. Mailer's Physiology, and especially 

 the English translation of the more recent 

 edition. The researches of Martin Bam/, in 

 1838 and 1839. The various contributions 

 of Bischojf] beginning in 1838 : His Systematic 

 Treatise on Development in 1842, and his 

 Monographs on the Development of the 

 Rabbit in 1842, of the Dog in 1845, of the 

 Guinea Pig in 1852, and of the Deer in 1855. 

 The researches of Coste beginning in 1833; 

 his work on Comparative Embryology in 

 1837, and his large and beautifully illustrated 

 work, as yet unfinished, beginning in 1850. 

 The works of C. Vogt on the Alytes Obste- 

 tricans (Batrachia) and on the Embryology 

 of the Salmonidae, in 1842. Lastly, the re- 

 cent and valuable researches of Remak on the 

 Development of Vertebrata in 1853-1855 ; 

 and the republication of R. Wagner's Icones 

 Physiologicas by Ecker. The works relating 

 to the invertebrate animals are much too 



numerous for quotation. I will only mention 

 the researches of Kolliker on the Cepha- 

 lopoda, of Qualrefages, Vogt, and others on 

 the Mollusca, Annelida, &c., and those of 

 J. Mil Her on the Echinodermata. 



I would also refer the reader to the excel- 

 lent report on the progress of discovery in 

 regard to the Ovum by Thomas W. Jones in 

 the Brit, and For. Medical Review for Oct. 

 1843, to Bischoff's article on the History of 

 Discovery in Development, and its application 

 to the explanation of Malformations in Wag- 

 ner's Dictionary of Physiology, to Leuck- 

 arfs Article on Generation in the same work, 

 and to Vrolik's Memoir on the Explanation 

 of Monstrosity from the History of Deve- 

 lopment, and to his article Teratology in this 

 Cyclopaedia. A large amount of information 

 on the whole of our subject will also be 

 found in C. Vogt's interesting Letters on 

 Living and Fossil Animals in 1851 ; in Victor 

 C orus 1 s System of Animal Morphology in 

 1853 ; in Van der Hceven's Manual of Zoo- 

 logy, with additions by Leuckart in 1850- 

 1856 ; and in the English works of Carpenter, 

 Owen, and Ri/mer Jones on Comparative 

 Anatomy and Physiology. 



In now bringing this article to a close, the 

 author owes an apology to the conductors 

 and the readers of this Cyclopaedia for the 

 extreme tardiness with which it has appeared. 

 The delay has arisen, in part, from personal 

 circumstances which need not be mentioned 

 here, and in part from the nature of the sub- 

 ject of which the article treats. In the ori- 

 ginal plan of the article, it was intended that 

 it should comprehend, along with the history 

 of the ovum, an account of the development 

 of the embryo. But as time advanced, and 

 every successive year added new and im- 

 portant matter to our knowledge of the science, 

 and greatly modified the statement of facts 

 previously regarded as established, it became 

 more and more difficult, especially in the 

 hands of one interested in the experimental 

 investigation of many of the individual facts, 

 to present a systematic and at the same time 

 clear and brief description of the researches 

 of physiologists on the subject of develop- 

 ment. The author regrets deeply that he 

 should thus be prevented from furnishing the 

 readers of the Cyclopaedia with this part of 

 the article as originally intended. But at the 

 same time he believes that when the recent 

 rapid progress of many departments of the 

 subject is considered, and the vast number of 

 details which would be required to embrace 

 even the shortest account of the origin and 

 formation of all the textures and organs of 

 the animal body, the knowledge of which 

 forms a science that is coextensive with the 

 whole range of anatomy and physiology, it 

 may be thought that he has in present cir- 

 cumstances judged rightly in abandoning the 

 attempt to compress into a limited space the 

 statement of so extensive and important a 

 branch of physiological inquiry. 



(Allen Thomson, M. D.) 



