Tate ; The Organization op " Daphnia Pulex." 135 



mutilated specimen has been met with during these investigations, 

 and in every instance individuals accidentally maimed died shortly 

 after. The moulting is very complete. The cephalic portion of the 

 carapace is first freed from the body, after which the animal draws 

 itself forward out of the remainder. Not only is the carapace cast 

 off, but the entire tegumentary envelopes of the arms, body and feet, 

 down to the minutest feathery fringe is removed uninjured, and the 

 shed exoskeleton, when fresh, forms a pretty microscopic object. 



The male Daphnia is distinguishable from the female by his 

 diminutiveness, by the absence of the dorsal cavity, by the elongated 

 articulated small antennae, and by two long bristles, produced from 

 the first pair of feet, constantly floating outside of the carapace. The 

 vam deferentia open upon the dorsal middle line of the last segment. 



The ovaries are situated along the sides of the intestinal canal of 

 the female, between the third and sixth articulations. The ova first 

 appear as small pellucid nucleated globules, and after a few days are 

 transferred to a clear space within the shell, on the back of the 

 animal, where they remain unattached, (their escape being prevented 

 by a tongue -like process arising in front of the sixth segment and 

 closing the posterior opening outwards) until the young have quitted 

 the eggs, undergone their first metamorphosis, and are capable of 

 shifting for themselves, when they are expelled. 



When first lodged within the dorsal marsupium, each ovum con= 

 sists of a central transparent nucleus ^ of its diameter, surrounded by 

 a granular mass of a bright greenish hue. The nucleus sub-divides, 

 forming a longitudinal row of globules, and the ovum elongates. The 

 alimentary canal is developed from each end simultaneously, and the 

 vitelline membrane or wall of the ovum is shed. The embryo then 

 lies in a sac which closely accompanies the dorsal outline of the 

 organism. The arms are evolved from the granular substance along 

 the ventral border of the sac, and lie closely appressed upon the sides 

 of the embryo. The eye specks next appear. The walls of the sac 

 are absorbed or transferred into a carapace, then the tail strikes out 

 vigorously, and the arms begin to flourish. Finally, the heart is 

 formed, and the circulation may be distinctly seen, the pulsations 

 often exceeding 300 per minute for some time before extrusion. The 

 time occupied in bringing about these changes, always equals the time 

 required for the stages of development within the ovary. If the ovum 

 quits the ovary, for example, on the sixth day, the young will leave 

 the parent on the twelfth day, but the length of time will vary with 



