438 F. W. GAMBLE. 



series, vol. xviii, p. 362. The most important additions to the 

 Turbellarian fauna are Oligocladus sanguinolentus and 

 Proceros argus. 



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 Acoela the 

 organ is quite simple, the ova elaborating their own food-yolk. 

 To such an organ I shall apply the term ovary. Certain 

 Rhabdocoela— 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 Cylindrosto- 

 minge and others occurs before the yolk is transferred to the 

 ova. To such an organ, performing a double function, the 

 Germans apply the term '' Keimdotterstock," and as an equi- 

 valent I shall use '^ gerra-yolk-gland," although, strictly 

 speaking, the word "gland" should apply to the vitelline 

 portion only. 



In the great majority of Turbellaria the two parts become 

 separate organs with distinct functions. For these I use the 

 old terms germarium for the ovarian organ, and vitella- 

 rium or yolk-gland for the nutritive one. The term vagina 

 I apply to that part of the female genital duct which forms a 

 sheath for the penis during copulation. For the storage and 

 nutrition of the spermatozoa various accessory organs are de- 

 veloped. For a single organ, serving to retain the sperm until 



