410 History of British Entomostraca. 



ovary, and gives it as his opinion that it is a disease these insects 

 are subject to, the effect of which is to arrest their future fecundity. 

 Straus, however, has been more fortunate in his observations upon 

 this very curious formation, and has found it to be a substance con- 

 taining two eggs, destined, he says, for the future generations of the 

 insect in the spring, these eggs resisting the cold of the winter, 

 which proves fatal to the perfect insect. Straus says, that they are 

 generally to be met with in the months of July and August. Ju- 

 rine mentions them as occurring as early as May ; and I have found 

 them in abundance upon the insect as late as the end of the month 

 of November. Jurine says, that after the third moulting has taken 

 place, we may see a green matter in the ovaries, which differs both 

 in colour and appearance from that of the eggs. After the fourth 

 moulting this green matter passes from the ovaries into the matrix 

 or open space on the back, and spreading forms the ephippium. At 

 first it is of a grayish colour, and some hours after becomes of a black 

 hue. When examined by the microscope it appears of a dense tex- 

 ture, composed of a sort of net- work of hexagonal cells. In the 

 centre of this opaque mass we see two round or rather ovular bodies, 

 placed one before the other, called ampullae by Straus, who says 

 that they are capsules opening like a bivalve shell. In each of 

 these ovular bodies is contained an ovum covered with a horny shell, 

 by which means they are protected from the cold of the winter, and 

 enabled to resist the severity of the winter which kills the parent. 

 At the next or fifth moulting, the Daphnia abandons the ephippium, 

 which floats on the surface of the water, and remains containing the 

 two eggs inclosed till next spring, when the young are hatched by 

 the returning warmth of the season. " These two species of eggs," 

 says Straus, " produced by the same animal, offer a very singular 

 example in the history of animals, and show with what wisdom na- 

 ture provides for the preservation of her smallest creatures." Straus 

 says, he has frequently hatched the young from these ova by sud- 

 denly bringing them into a warm temperature. In the months of 

 November and December, I ascertained the truth of Straus's state- 

 ment, and witnessed the young hatched from these ephippial eggs 

 by keeping them in my room. November 2d, I took several ephip- 

 pia which I found floating on the surface of a saucer full of water 

 containing D. pulex, numbers of which had ephippia attached to 

 them, and placed them by themselves in a wine glass of clear water. 

 10th November, two young ones born. 16th, one more. 29th, two 

 more born. 21st, one more. 23d, two more. November 29th, took se- 



