250 Mr. Darwin on several Planarise. 



and form a single, elliptic, sinuated body. These two mouth- suckers 

 are quite similar ; they are much shallower than those of any other 

 species of the family which I have seen ; their membranous edges 

 are very thin, narrow, transparent and sinuous : in the act of con- 

 traction they become folded in a complicated manner, like the bud 

 of a flower. I was able easily to dissect them out of the body, and 

 they retained, in the characteristic manner described by Duges, and 

 as in the terrestrial Planarice, an extreme degree of irritability and 

 contractile power, long after the rest of the body had ceased to live. 



In the elliptic space surrounding the two mouth- suckers when 

 contracted, and between the mouths of the lateral, branching, intes- 

 tinal cavities, innumerable ova are arranged in groups, from two to 

 four in each ; these are represented in the drawing only by double 

 dots. These ova were easily separated ; they are spherical, jj^ths 

 of an inch in diameter, and contain a central opake mass. In the 

 posterior clear space there are two minute, but quite distinct, orifices 

 (D and E), which I do not doubt are the reproductive pores : into 

 this clear space a large fork, filled with opake white matter, enters, 

 as is shown in the drawing ; this matter consists of minute, white 

 globules in chains, imperfectly united together : I believe these are 

 immature ova, and hence I suppose that the fork is the ovarium, from 

 which the ova pass into the clear spaces surrounding the mouth- 

 suckers and are there matured. 



The ocelli are black and circular, and are arranged in four groups, 

 two of which are round, and two in elongated bands inclined to each 

 other : the ocelli in the bands are not seated on the dorsal surface, 

 but deep within the body, near the ventral surface. Colour pale 

 " tile-red," darkest on the dorsal ridge, with colourless spaces over 

 the genital orifices and over the ocelli. Length -^jths of an inch ; 

 breadth of anterior part of body xo tns > °* posterior part r \jth of an 

 inch. 



Hab. Under stones in tidal pools, Chonos Archipelago (Western 

 S. America) (December). 



This animal is very active, can crawl quickly, and can swim 

 well by the movements of its thin marginal edges : it can adhere 

 firmly to stones. 



This is the most complicated and singular form of the large 

 family of Planarice which I have seen or met with described. The 

 presence of two alimentary orifices and two mouth-suckers is an- 

 other and interesting point of affinity between the Planarice and 

 the true parasitic worms, in which the number of mouths so often 

 exceeds one. I believe that the presence of the large forked ova- 

 rium, and of groups of ocelli situated at different depths, are pe- 

 culiarities of structure confined to this genus. If the small mass 

 protruded from the posterior orifice (D) of the Planaria (?) m- 

 cisa was really a small contracted mouth-sucker, this species is 

 closely allied to our present new genus ; with the chief difference 

 of the two genital orifices being near the anterior, instead of the 

 posterior extremity. 



