460 A. E. Verrill — Marine Planarians of JVeic Mngland. 



by some special treatment, such as that mentioned above. When 

 thus treated it is usually possible to identify most of the larger 

 dendrocoelous planarians, but some of the smaller and more contrac- 

 tile species and most of the Rhabdocoela cannot be determined from 

 alcoholic specimens unless studied in thin sections — a method requir- 

 ing much time and giving rather uncertain results for specific identi- 

 fication. Such species should, therefore, be studied as fully as 

 possible while living, and preserved by special methods on micro- 

 scopic slides, so as to show their anatomy. 



1 have recently gone over the collections of planarians preserved 

 in the Museum of Yale University and those contained in the collec- 

 tions made by the U. S. Fish Commission during many years and 

 have identified most of the larger specimens.* 



The planarians (Turbellaria) may be divided into three orders, 

 viz : 



I. Dendroocela. In these the stomach has more or less numerous 



branches, often forked or arborescently divided ; the body is 

 usually rather broad and flat. Size usually large. 



II. Aca-:LA. In these there is no digestive organ distinct from the 



body-cavity. The mouth opens into a space lined with the 

 body-pai'enchyma, and without any .definite bounding mem- 

 brane. The body is soft, changeable, usually flat. Size small. 



III. Rhabdoccela. In these the stomach is unbranched, and usually 

 more or less cylindrical in form, but without an}- anal pore. 

 Form of body various, often thick-ovate, and even linear. As in 

 the preceding groups, the species are nearly all hermaphrodite. 

 The reproductive organs are very complicated and vary greatly 

 in structure and position in the various genera and families, so 

 that they afford very important chai-acters for classification. 

 The mouth occupies various positions : anterior, medial ventral, 

 posterior ventral, etc. Size ver}^ small. Fluviatile and marine. 



The Dendrocoela are divided into two suborders, viz : 

 I. DiGONOPORA or Polycladidea. In these there is a central 

 stomach from which several main branches go forth on each 



*In this article all specimens recorded as collected between 1871 and 1887, unless 

 otherwise stated, were collected bj- myself and others of the U. S. Fish Commission 

 parties. The numbered stations recorded are those of tlie U. S. Fish Commission 

 dredgings, made, for the most part, while I had personal charge of that part of the 

 work of the Commission. The specimens from Eastport and the Bay of Fundy, prior 

 to 1872, and those recorded from Long Island Sound were mo.stly collected by me for 

 the museum of Yale Uuiversitj-. 



