, Pp is < Cte +) Sib eee TOC SAN » 
Ch p Hae LOE SAY Basten Oo) Ab 
\ b ‘ : q it ee: 
328 GEOL. AND NAT, HIST. SURVEY OF MINNESOTA. 
ond pair of legs. In stage B the post-abdomen has developed the per- 
manent number of set, but the ratio of the length of the terminal 
seta to the length of the body of the member is much greater than in 
the adult. In passing through stages C and D, the parts of the RO 
abdomen gradually assume the proportions of ahve 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 was isolated in saucers of water and a record 
kept of the number placed in each 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 larval stages which were placed in this water — 
were examined from time to time. In every case the specimens devel 
oped 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 morphological differences between 
stage A and the adult are differences, not only in the shell structure, 
but also in the structure of the post abdomen. And these differences 
are aS great as those between the genus Cypris and the genus Oypri- 
dopsis. These facts show that shell structure of Ostracodes, when taken 
alone, is of almost no taxonomic 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 in 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-abdo- 
men. Inthe genus Cypridopsis the body of the post-abdomen is but 
slightly developed, while the sete are quite long. In stage A, in the 
larval history of Cypris herricki the post-abdomen is in this rudiment- 
ary condition; thus it corresponds very closely to the genus Cypridop - 
sis. Not only that, but the unbanded forms of this stage correspond 
very closely to Cypridopsis hystrix Herrick.* Indeed, when this stage 
y, Bates L. Herrick. Contribution to the Fauna of the Gulf of pitts: and theSouth. 1887. P.30, Pl 
ig. 6 
