258 Royal Society. 



the receptacle formed by the new carapace. The ephippium is 

 cast with the rest of the skin, from which however it soon becomes 

 detached, and continues to form an efficient protection to the eggs 

 until they are hatched. These eggs probably require to be fer- 

 tilized, but this fact is not completely proved. With one ex- 

 ception, whenever the author observed ephippia, he could also find 

 males ; and, generally speaking, the numbers of each were in pro- 

 portion to one another. Impregnation is not, however, absolutely 

 necessary to the production of ephippia, as the author has now in 

 his possession three ephippia, formed by isolated females. It re- 

 mains to be seen whether young will be developed from these or not. 



The early stages of the agamic egg are very similar to those of the 

 ephippial egg, and consist of the enlargement, in the front part of the 

 ovary, of one of the ovarian cells, which then becomes a germinal 

 vesicle, and the deposition round it of granules, with the addition in 

 this case of oil-globules. This process continues, the other two or 

 three cells which may have existed in the same ovarian mass gradu- 

 ally disappear, and there is thus formed an egg-like mass, consisting 

 of a germinal vesicle, minute dark granules, and large oil-glo- 

 bules. When the growth is nearly completed, the vitelline mem- 

 brane is added. This is at first very delicate, but after deposition in 

 the receptacle soon becomes hard. The ovarian eggs of Daphnia, as 

 well as those of Cypris, never contain round masses like those of 

 Aphis and Musca ; but after their entry into the receptacle, yelk- 

 masses are found, homologous with those present at the corresponding 

 periods in Phryyanea'^' . The eggs when laid are about -gf^ of an 

 inch in diameter ; they gradually become ^1%q, when the vitelline 

 membrane splits and falls off, and the young animal is hatched. Far, 

 however, from resembling its parent at this time, the young Daphnia 

 is a spherical bag, inside which the formation and development of 

 the new organs is rapidly progressing f. Instead therefore of under- 

 going no metamorphosis, the young Daphnia only assumes the well- 

 known characters of the genus after the first changes of skin. The 

 author proceeds to compare this phaeuomenon with a similar one 

 observed by Mr. Spence Bate in Gammarus, by Prof. Huxley m 

 Mysis, by Dr. Cohn in Sphceropleu, in many Annelids, and in the 

 interesting entozoon Monostoinum mutabile. The young Daphnia at- 

 tains a length of "025 inch before it leaves the receptacle of the mother, 

 but the length of time durhig which it remains therein varies ac- 

 cording to the temperature. The author has never met with an ex- 

 ception to the rule noticed by preceding writers, that unisexuality is 

 characteristic of an agamic brood. 



It follows from these observations, that the self-fertile Daphnise 



* The round balls desciibed by Herold in the ovarian eggs of Bomlyx, appear 

 to be of a ditfereut nature, and homologous with the Nahrungsdotter mentioned 

 by Carus in spiders' eggs and the oil-globules of Daphnia. 



f It is worthy of notice, that the back fold indicating the divisions between the 

 head and body is opposite the line between the mandibles and the first pair of 

 maxillae, which latter appear therefore to belong to the body, as Zaddach also 

 asserts, and not to the head. 



