OVUM. 



the yolk ; and Bischoff states that they gra- 

 dually disappear, or are dissolved without 

 obvious change. We are at a loss to deter- 

 mine what office these globules may have in 

 connection with the changes of the ovum at 

 the time they appear. 



Lastly, I would notice the interesting re- 

 lation which appears to subsist between the 

 situation of the germinal vesicle and the cen- 

 tre of the germinal membrane afterwards 

 formed, or the germinal pole of the ovum, 

 and the conformity in the direction of the 

 line of the first cleavage of the yolk with that 

 of the principal axis of the embryo in verte- 

 brate animals. The first fact has been observed 

 in all animals, and the latter has been ascer- 

 tained by Mr. Newport's researches in Ba- 

 trachia, and by observations which I have 

 myself made in the bird's egg during its de- 

 scent through the oviduct. These facts, as 

 yet inscrutable in their nature, point to in- 

 teresting laws relating to the connection of 

 the first phenomena of development, which 

 may be worked out by the further prosecution 

 of these inquiries. 



In the preceding part of this article we 

 have considered chiefly the anatomical struc- 

 ture of the ova of animals, and have made 

 little mention of their chemical composition. 

 The knowledge of the latter subject is as yet 

 very imperfect. In a recent Memoir* Messrs. 

 Valenciennes and Fremy have given an ac- 

 count of an extended series of experimental 

 researches in which they have been engaged, 

 with a view to determine the differences in 

 the chemical composition of the ova of dif- 

 ferent animals, and although this investigation 

 is still necessarily incomplete and fragmentary, 

 they appear already to have arrived at some 

 interesting results. The following are some 

 of the more important of these results. 



The albumen or white is not exactly of 

 the same composition in the eggs of different 

 birds ; but it generally contains albumen with 

 salts and a compound of sulphur in solution. 

 In the yolk of birds' eggs they recognise the 

 principle first distinguished by Dumas and 

 Cahours as Vitelline, a substance precipitable 

 by mixture with a large quantity of water, 

 and apparently more nearly resembling fibrine 

 than albumen in its composition and some of 

 its properties. The phosphuretted fat of the 

 yolk is somewhat similar to the cerebral fatty 

 matter. 



The glairy white of the eggs of cartilagi- 

 nous fishes is very different from that of birds' 

 eggs, being neither soluble in water nor coa- 

 gulable by heat nor acids to the same degree. 

 It seems to contain only traces of organic 

 matter. The angular and tabular particles 

 of the yolk of cartilaginous fishes are com- 

 posed of a principle which these authors re- 

 gard as peculiar, and have named Iclithinc. 

 This substance is insoluble in water, alcohol, 

 and ether, and, on being dissolved by hydro- 

 chloric acid, gives no violet colour, as albu- 

 men does. It is dissolved by all the concen- 



* See Journal cle Pharmacie, &c., vol. xxv. pp. 

 321. and 415., and vol. xxvi. p. 5., 185"4. 



[141] 



trated acids, and by dilute acetic and phos- 

 phoric acids. Its composition is stated to 

 be as follows ; carb. 51 ; hyd.^6'7 ; nit. 15; 

 ox. 25'<i ; phosph. I'D. 



In the ova of osseous fishes these authors 

 do not find the same organic principle, but 

 have detected two others in variable propor- 

 tions. One of these, which they have named 

 Ichthidme, exists only in small quantity, and 

 is absent in some fishes : it is quite soluble 

 in water. The other which is more generally 

 prevalent and in larger though variable quan- 

 tity is precipitated by water into a viscous 

 substance. This has been named Ichthulinc. 

 Messrs. Valenciennes and Fremy have ascer- 

 tained the interesting fact that while these 

 principles, especially ichthuline, exist in large 

 quantity in the ova at an early stage of their 

 growth in the ovary, they gradually diminish 

 in quantity or are changed as the ova ap- 

 proach maturity, and give place chiefly to 

 albumen, which holds the phosphuretted fat 

 in suspension. In the salmon's egg there is 

 a large proportion of ichthuline, which is the 

 cause of their becoming opaque when water 

 enters the yolk. These authors propose in- 

 deed this character as a test of the maturity 

 of the ova, as they are not rendered opaque 

 by water when mature. It would be inte- 

 resting to know whether fecundation produces 

 any immediate chemical change on the prin- 

 ciples of the yolk. The composition of ich- 

 thuline is stated to be as follows : carb. 52'5 ; 

 liyd. 8 ; nit. \5'2; ox. 22'7 ; phosph. 0'6 ; 

 sulph. 1. 



The ova of Batrachia seem to resemble 

 most nearly those of cartilaginous fishes, in 

 so far that the tabular particles of the yolk 

 are composed of ichthine. The external ge- 

 latinous covering is described as a tissue of 

 hyaloid membrane which absorbs water in a 

 determinate quantity. 



The ova of Ophidia and Sauria resemble 

 nearly those of birds in the composition of 

 the white and yolk, containing the principle 

 vitelline in the latter. The yolk of the Viper 

 presents the singular peculiarity of becoming 

 gelatinous by immersion in water. 



In the ova of several Chelonia they have 

 detected a different principle from vitelline to 

 which they give the name of vitelline. This 

 principle is soluble in potash, and has the 

 following composition: carb. 4D'4; hyd. 7'4; 

 nit. 15'ti ; ox. and phosph. 26'7. 



Among the invertebrate animals Messrs. 

 Valenciennes and Fremy have examined the 

 ova in several classes. In the Crustacea 

 they have given much attention to the in- 

 vestigation of the curious colouring principle 

 of the ova, which appears to be the same as 

 that existing in the shell, and which being 

 green in the moist state passes into red in a 

 variety of circumstances. They have isolated 

 this colouring matter by a very simple pro- 

 cess, and give an interesting account of its 

 properties, especially of the circumstances 

 causing it to change to red, such as the ac- 

 tion of alcohol, boiling, desiccation, placing 

 in a vacuum, friction, &c. 



The ova of Arachnida and Insects are 



