RECENT WOEKS 01^ THE E^TTOZOA. 337 



their full description demands a separate article. Anatomists differ 

 miicli in their interpretation of these "vessels," and in their at- 

 tempts to correlate the diverse arrangements which they present 

 among the leading genera and orders of Helminths. The same, un- 

 happily, may still be said of the structures of these animals in 

 general. 



Three periods may be traced in the history of Helminth ology, 

 corresponding in some degree, to similar periods which have marked 

 the progress of zoology in general. 



The first, or tentative period, during which observations of all 

 kinds were being accumulated, without due regard to completeness, 

 accuracy, or orderly arrangement, may be said to have closed with 

 the commencement of the present century. 



The two next periods are nearly conterminous, and the com- 

 mencement of both was foreshadowed in the writings of Goeze,* who 

 may, however, arbitrarily be referred to the first period. 



The second, or systematic period, is easily dated from the 

 publication (1808-10) of the ' Entozoorum Historia Naturalis' of 

 Rudolphi, a naturalist strongly imbued with the opinions of his great 

 master, Linnseus. In 1819 appeared a condensed revision of this 

 work under the title ' Synopsis Entozoorum.' Many minor essays 

 on systematic Helminthology soon followed, among which those of 

 Nitzsch, Creplin, and E. S. Leuckart especially claim attention. All 

 these, however, had to give way to the ' Histoire Naturelle des 

 Helminthes, ou Yers Intestinaux,' of Dujardin, published in 1845, 

 as one of the volumes of the Nouvelles Suites a Buffon. A third 

 great general work was the ' Systema Helminthum' of Diesing (1850), 

 wlio lias, in addition, written a series of most valuable memoirs on 

 the several tribes of these animals, of the systematic characters of 

 which he may justly be deemed the prime living expositor. 



The third, or anatomical and embryological period, commenced 

 later than the second, and, in spite of all it has accomplished, is yet 

 in comparative infancy. Yon Baer,t the father of modem em- 

 bryology, was also the first to promote the deeper study of the 



* Versuch einer Naturgeschichtes Eingeweidewurmer der tMerischer Korper, 

 1787. 



t In his ' Beitrage zur Kenntniss der Niederen Thiere' (1827), containing many 

 curious observations on the Trematoda. 



N.H.R.— 1865. 2 A 



