PLATYHELMINTHES TURBELLARIA 



similar to those of certain Khabdocoelida (e.g. Monotus, Fig. 19, 

 I)), enabling it to cling tightly to the Zoster a, and so to resist 

 the loosening action of the waves. 



The movements of Land Planarians are somewhat peculiar. 

 The ventral surface of Bipalium has a median groove, into 

 which the ducts of numerous mucus -glands open. This is 

 bordered by two ridges clothed with long and powerful cilia, 

 which perform the chief part in propelling the animal, aided, 

 according to Lehnert, 1 by muscular waves which pass from the 



FIG. 16. Suckers of Tri- 

 clads. A, Planar ia 

 punctata Pall. , a, dorsal 

 surface of head ; b, ven- 

 tral surface (freely mov- 

 ing) showing the sucker ; 

 c, sucker contracted 

 (after Hallez) : B, ven- 

 tral surface of head of 

 Dicotylns pulvinar Gr., 

 from Lake Baikal (after 

 Grube) : C, dorsal sur- 

 face of Procotylea fivri- 

 atilis Gir. (after Girard ) : 

 D, sucker of Cotyloplana 

 whiteleggei Sp. (after 

 Spencer) : E, ventral 

 view of head of Plan- 

 aria alpina Dana (pre- 

 served specimen) ; hy, 

 adhering groove ; m, 

 thickened musculature 

 forming the margin of 

 the sucker ; sc, sucker ; 

 t, tentacles. 



head, backwards, i.e. opposite in direction to those by which a 

 snail slides along. This observation, however, needs confirma- 

 tion. The whole body executes sinuous movements, during which 

 the crescentic head, lifted slightly above the ground (Fig. 15, A), 

 is constantly altering and regaining its normal shape, somewhat 

 as a Planaria lactea uses the lobes of its head. Further ex- 

 amination shows that the margin of the. head of Bipalium is not 

 only provided with eyes, but in addition, with ciliated, (probably) 

 olfactory pits. Such depressions, innervated directly from the 

 cerebral ganglia, have been found in sixteen species of Geoplana, 



^Archivf. Naturgesckiclitc, 57 Jahrg. Bd. i. Hft. 3, 1891, p. 308. 



