14 BULLETIN OF THE LABORATORIES 



than in the adult. In passing through stages C and D, the parts of 

 the post-abdomen gradually assume the proportions of the adult. 



Every precaution has been taken to be sure that all the stages 

 above described were stages of one and the same animal. A definite 

 number of each stage were isolated in saucers of water and a record 

 kept of the number placed in edch saucer, and also of the stage of 

 growth exhibited by each set at time of isolation. The water used 

 was collected from a pool which did not contain any Ostracodes which 

 in the least resembled those under consideration. As a further pre- 

 caution the water was allowed to stand in the laboratory a couple of 

 weeks. The loss in volume was replaced by river water, taken from 

 the city hydrant. I never have found any Ostracoda in said river. 

 Thus there was no possibility of the water containing the eggs of 

 Cypris Herricki, The larvae stages which were placed in this water 

 were examined from time to time. In every case the specimens 

 developed into the adult form. 



The morphological differences between the shell of stage B and 

 the shell of stage A, and between the shell of stage B and the adult 

 are certainly as great as the morphological differences between the 

 shells of closely allied species. The mor])hological differences be- 

 tween stage A and the adult are differences, not only in the shell 

 structure, but also in che structure of the post-abdomen. And these 

 differences are as great as those between the genus Cypris and the 

 genus Cypridopsis. These facts show that shell structure of Ostra- 

 codes, when taken alone, is of almost no taponomic value. 



These facts also have phylogenetic significance. These various 

 larval stages are resting stages in the development of Cypris Herricki. 

 Since it is true that the ontogenetic development of an individual is a 

 rapid and compact repetition of its phylogenetic history, these larval 

 forms must represent past stages m the evolution of Cypris Herricki. 

 As has been stated above, stage A corresponds very closely to the 

 genus Cypridopsis. The main distinction between the genus Cypris 

 and the genus Cypridopsis is the difference in the form of the post- 

 abdomen. In the genus Cypridopsis the body of the post-abdomen is 

 but slightly developed, while the setae are quite long. In stage A, in 

 the larval history of Cypris Herricki the post-abdomen is in this 

 rudimentary condition; thus it corresponds very closely to the genus 

 Cypridopsis. Not only that, but the unhanded forms of this stage 

 correspond very closely to Cypridopsis hystrix, Herrick. ' Indeed, when 



^ C. L. Ilerrick, Contribution to the Fana of the Gulf of Mexico and 

 the vSouth, 1887. p. 30, pi. IV, fig. 6. 



