ON HETEROPLANA. 203 



On Heteroplana, a New Genus of Planarians. 



By 

 Ai-tliiir IrVilley, D.Sc. 



Since I have been in Lifu I have obtained one specimen 

 only of a very remarkable flat-worm which must form the 

 type of a new genus and a new family. The quite unexpected 

 relations of symmetry presented by this form, which I will 

 call Heteroplana, speak for the accuracy of the observations, 

 although I should be more satisfied if I could obtain more 

 examples of it. 



Heteroplana presents externally a sub-symmetrical ap- 

 pearance, but in its structure it is characterised by what may 

 be roundly described as the atrophy of the left half of the 

 body. The left intestinal diverticula are aborted. The 

 mouth is placed at the middle of the length of the body, but 

 approximated to the left margin. The cerebral ganglion is 

 similarly approximated to the left margin. Through the 

 whole body, and especially prominent in the anterior and 

 posterior regions, is a close reticulum formed by the anasto- 

 mosis of fine moss-like tubules which probably constitute the 

 genital apparatus. 



I had the specimen under observation for a comparatively 

 long time, and made several drawings from it, one of which I 

 enclose. On account of its remarkable relations of symmetry 

 I should place this genus in the order Archiplanoidea, esta- 

 blished by me for the reception of Cceloplana and Cteno- 

 plana, because, although it is very difi'erent from the two 

 latter forms, yet it would appear to be more nearly related to 

 a biradial type than to a bilateral type like the Planarians. 

 This seems to follow from a consideration of such a form as 



