RRITISH MARINE TURBELLARIA. 185 



Museum ' appeared. The marine Turbellaria are taken from the works 

 of Johnston, Thompson, and Dalyell, together with a few new records. 

 A year later Lankester (39) issued a list of the fauna of Firman 

 Bay, Guernsey, containing Convolutaparadoxa, Leptoplana auricularis, 

 L. fiexilis, and Eurylepta cornuta. In 1875 Mcintosh (45) published 

 his ' Marine Invertebrates and Fishes of St. Andrews,' in which several 

 Turbellaria are mentioned. The occurrence of Prostoma lineare Oe. 

 (Gyrator herniaphroditus, Ehrg.), in the sea, and a short description of 

 Mesostoma bifidum, n. sp. (Pseudorhynchus bifidus), are specially note- 

 worthy, v. Graff paid a visit to Millport, the result of which are 

 incorporated in his great monograph ([53,] 1882, p. 437). Twenty- 

 four marine species of this group were found and fully described. In 

 the summers of 1884 and 1885, Koehler explored the Channel Islands. 

 A list of the forms obtained may be found in the ' Annals and Mag. 

 of Nat. Hist.,' fifth series, vol. xviii, p. 362. The most important 

 additions to the Turbellarian fauna are Oligocladus sanguinolentus and 

 Proceros arc/us. 



3. Nomenclature. 



I wish in this section to discuss certain difficulties connected 

 with the terminology of the complicated reproductive organs of the 

 Turbellaria. 



The stages exhibited by different members of this group, by which 

 a simple organ, producing ova capable of manufacturing the necessary 

 food-yolk, becomes differentiated into two parts, one furnishing ova, 

 the other yolk, and the final separation of these two parts into two 

 distinct organs, have been pointed out by Gegenbaur, Balfour, and 

 others. Thus in the Accela the organ is quite simple, the ova 

 elaborating their own food-yolk. To such an organ I shall apply the 

 term ovary. Certain PJiabdocada — e. g. Prorhynchus — exhibit the 

 first stage in complexity. The cells are still equivalent, but are not 

 all equally capable of becoming ova ; those that are not, form 

 yolk-cells destined for the nutrition of the ovarian part of the organ. 

 The secretion of yolk-granules by the yolk-cells surrounding the 

 fertilised ova, which in this form does not take place until the ova 

 have undergone segmentation, in the Gylindrostominm and others 

 occur before the yolk is transferred to the ova. To such an 



