PREFACE. 



The exhaustion of the edition of "A Final Report on the Crustacea 

 of Minnesota included in the Orders Cladocera and Copepoda" has 

 led to a demand for republication. It has seemed unfortunate that 

 the imperfections of this work, many of them due to the unsatisfactory- 

 state of the European literature, while others were the result of im- 

 perfect information and faulty observation or hasty judgment, should 

 be perpetuated. The original paper grew out of studies made chiefly 

 while the author was an undergraduate at The University of Minne- 

 sota and was very fully occupied otherwise, and circumstances have 

 prevented him from anything but the most casual pursuit of the sub- 

 ject since 1884. It might have appeared that the work had served its 

 purpose, but there were many indications of a need for a comprehen- 

 sive, synoptical survey of this field, and the present paper seemed the 

 only approximation to such a work. A serious illness, which has 

 greatly impeded the progress of the revision at last decided on, has 

 at the same time made it possible by forcibly relieving the author of 

 more pressing duties. It would have been a great satisfaction to him 

 to have given to the subject the thorough field work and comprehen- 

 sive bibliographic elaboration it deserves, but strength and opportu- 

 nity forbid. In default of this it might seem wiser to enumerate only- 

 American species, but experience has shown that geograj^hical limi- 

 tations do not prevail to any great extent in most of the families here 

 considered. In such instances, Calanidw for example, the attempt 

 has been made to include all valid species and a full synonomy. In 

 the others as full a list is given as is now possible, and while this 

 work may not be alone sufficient to enable the specialist to formulate 

 new diagnoses and descriptions, it yet offers a*much fuller synopsis 

 than yet published and will give a bird's-eye view of the taxonomy of 

 the subject. 



The most important aspect of the subject, namely, the biological 

 relations of these organisms, has been too generally neglected. In no 

 other group can the problems of parthenogenesis and heterogenesis 

 be so easily and accurately studied. The transparency of the body 



