ZOOLOGY: W. J. CROZIER 
379 
2 Goldschmidt, R., Zs. ind. Abs.-Vererbungslehre, 7, 1912, (1-62); also these Proceedings 
2, 1916, (53-58). 
3 Called sex intermediates by Riddle; intersexual forms by Goldschmidt. 
4 There is one reference in the literature to androgynous Cladocera (in Daphnia atkin- 
soni). Judging from De la Vaulx's description these individuals, which he called gynandro- 
morphs, were almost certainly sex intergrades. 
6 Banta, A. M., these Proceedings, 2, 1916, (578-583). 
6 The writer used the terms female and male with the mental reservation that inas- 
much as femaleness and maleness are now definitely known to be relative in some cases 
they may be relative in all individuals and that the terms female and male are themselves 
to be considered relative not only in Cladocera, pigeons and moths but perhaps also in all 
animal and plant forms in which sex is known to occur. 
7Vaulx. "R dp la. Bull. Soc. Zool. France, 40, 1916, (102-104, 194-197, 
ON THE METHOD OF PROGRESSION IN POLY C LADS 1 
By W. J. Crozier 
Bermuda Biological Station for Research, Dyer Island, Bermuda 
Communicated by E. L. Mark, October 29, 1918 
Turbellarians are able to make progress through the water by means of 
muscular movements of the body as a whole, or of its lateral extensions; their 
creeping progression on a solid substratum, however, has usually been attrib- 
uted to the action of cilia. According to Stringer (191 7), 2 the locomotion 
of planarians is effected by muscular contractions, which may be organized 
after the manner of the locomotor wave upon the foot of a monotaxic gastropod 
(cf. Parker, 191 1), 3 the ciliary activity taking no necessary part in the loco- 
motion. Some observations, which may here be briefly noted, tend to con- 
firm the nature of this finding, and add to the variety of known muscular 
creeping movements in turbellarians. 
One species of Leptoplana, occurring at Bermuda in moderate numbers, 
differs from the more frequently encountered L. lactoalba Verr., approaching 
more nearly the form L. lactoalba var. tincta Verr. It is found on the under 
surfaces of stones, near high water level, and is commonly about 3.5 cms. 
long. If, out of water, a stone bearing one of these leptoplanas is turned 
over, exposing the animal to light, it creeps about upon the moist surface. 
The worm also creeps rapidly under water, and in addition is a vigorous 
swimmer. It has usually been believed that in Leptoplana " creeping is a 
uniform gliding movement, caused by the cilia of the ventral surface, aided 
perhaps [how?] by the longitudinal muscle layer of this surface" (Gamble, 
1901, p. 10) . 4 While this may very well seem to be the case in L. tremellaris 
(Gamble, loc. cit), and in several other species which I have observed, it is 
distinctly not true of the form which I may refer to as L. 'tincta.' The 
ventral surface of this platode is richly ciliated, and in creeping it deposits 
an appreciable slime-track, such as that in which the cilia of triclads have 
