EEPORT OF THE SECRETARY. 13 



apart, and prosecuting studies of a similar character, without the knowl- 

 edge of other labors than their own, were brought into relations of 

 correspondence and exchange, and thus, by their mutual sympathy and 

 support, and by the concentration of effort on the part of each to some 

 special line of research, the common interest of science was advanced. 

 We regret to say that after many years sojourn in this country, Baron 

 Osten-Sacken has returned to Europe, where, however, his assistance 

 is continually invoked by entomologists desiring information in regard 

 to type specimens, books not procurable in the United States, &c, 



The list of Diptera aforesaid (published in the Miscellaneous Collec- 

 tions) brought together a mass of references to the descriptions of about 

 1,800 species, scattered in more than one hundred different works 

 and scientific papers. Such a publication was an indispensable prelim- 

 inary step before any study of the diptera could be attempted. This 

 formed the first of a series of works undertaken by the Institution to 

 facilitate the study of entomology, which has included diptera, coleop- 

 tera, lepidoptera, neuroptera, and hymenoptera. 



During the past year the work of Baron Osten-Sacken, much extended 

 by his later critical studies, has been republished by the Institution. 

 This new edition of the work is not merely a revision of the catalogue 

 published twenty years ago; but it is an entirely new one prepared on 

 a different plan. The difference between eleven and sixty-sir, the num- 

 ber of species of one genus, Tn/pcta, represents the addition made to 

 our knowledge during the interval between the two catalogues. Other 

 genera give similar results. Another important difference between the 

 old and new catalogues consists in the fact that the majority of the 

 species enumerated in the latter are represented in a collection now in the 

 Museum of Comparative Zoology in Cambridge, Mass., which contains 

 over 2,000 named and described species of diptera from North America. 

 The region embraced in the present catalogue is the whole of ISTorth 

 America, including the West Indies. It has been the effort of the 

 author to make sure that every name in the list should actually rep- 

 resent a different species. To attain this result, he visited and examined 

 the museums in London, Paris, Lille, Berlin, Frankfort, Darmstadt, 

 Turin, and Vienna. Of all orders of insects the diptera offer probably 

 the most difficulties to the describer, arising from the. minuteness of the 

 characters on which generic and specific distinction are based. Each 

 family requires a special study, and a dipterologist may be very well 

 versed in some families, without being able to express any opinion with 

 regard to questions concerning others. In the introduction to the cata- 

 logue, the author presents some recommendations as to the best course 

 to be pursued in the study of diptera, and advises specialization. 

 Amateurs may collect and name specimens, but should not publish 

 anything until they have chosen some single family and nearly ex- 

 hausted it by study and collecting. "The exhaustive study of a single 

 family is far more remunerative both in pleasure and in usefulness 



