American journal of physiology . pathicreactions of certain Crustacea.^ cr. 11. Animals Experimented with and MethodsOF Collecting. During the fall of 1898 Simocephalus vetulus, a Cladoceran verysimilar to Daphnia pulex, existed in abundance in several small ponds in Cambridge, butDaphnia were scarce. Lastfall the reverse was pulex (Fig. i)swarmed in certain places,while Simocephalus wasfound in small numbers. The material for the fol-lowing work, both DaphniaFigure 1. — Daphnia pulex DeGeer. X 13. and Cypris, was obtained inat. antenna; atl. antennule ; ,s;l. d.

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American journal of physiology . pathicreactions of certain Crustacea.^ cr. 11. Animals Experimented with and MethodsOF Collecting. During the fall of 1898 Simocephalus vetulus, a Cladoceran verysimilar to Daphnia pulex, existed in abundance in several small ponds in Cambridge, butDaphnia were scarce. Lastfall the reverse was pulex (Fig. i)swarmed in certain places,while Simocephalus wasfound in small numbers. The material for the fol-lowing work, both DaphniaFigure 1. — Daphnia pulex DeGeer. X 13. and Cypris, was obtained inat. antenna; atl. antennule ; ,s;l. d. dorsal gland ; a small rain-water pond thatfr. heart; ^rj. zVm^. brood pouch; J-*/, t-a. caudal 1 1 • , 1 • , spine; oc. eye. presumably IS dry durmg the summer. Here Daphniacould be seen in large numbers on the sunny side of the pond andCypris virens (Fig. 2) abounded in the grass and mud of the bottom. ^ Towle: This journal, 1900, iii, p. 352. 2 An account of this work (4) will be given in the next paper of this

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