1914.] NATURAL SCIENCES OF PHILADELPHIA. 427 



tentacles, Avhich are in the position of the ears of the moose. The 

 foot, when fully protruded, is attached firmly to the surface moved 

 over; the proboscis is then raised and waved about again, and crawling 

 commences. The progression begins by a stretching forward of the, 

 proboscis, its tip is then applied to the surface moved over, and this 

 tip flattens out until nearly the size of the foot. If the proboscis 

 secures a firm attachment, the foot may now be released, and either 

 drawn up to the attached proboscis by sliding the edge of the foot 

 along the surface, or the entire animal may be supported upon the 

 proboscis and the foot raised clear of the surface and drawn up to 

 the proboscis, when its edge will rest on the surface moved over. 

 Perhaps more often the foot is raised anteriorly and slid forward 

 upon its posterior edge up to the attached proboscis; the position 

 assumed by the body of the animal being now the same as when 

 it is retracted into the shell. Starting from this position, the method 

 of progression may be described as follows: The square pad of 

 the foot is turned down anteriorly until it is firmly attached to the 

 surface moved over, simultaneously the attachment of the proboscis 

 is released and this is moved to find another attachment; as soon 

 as this is found the firm attachment of the proboscis is effected again ; 

 then the entire shell is hitched forward as the foot is lifted and 

 brought up in contact with the under side of the proboscis. In 

 case the foot is lifted clear of the surface moved over, the posterior 

 edge of the foot touches the surface first; if not lifted clear of the 

 ground, this edge is slid or dragged over the surface until the foot 

 comes up to the under side of the proboscis. Its posterior edge is 

 then applied to the ground, and, as the proboscis is loosened and 

 raised, the foot turns down until it is firmly in contact with the 

 ground, and the waving about of the proboscis and its final attach- 

 ment proceeds as before. 



The entire cycle of movements comprising the "step" is executed 

 in four seconds. or less, so that the animal will make 15 to 17 "steps" 

 in a minute when advancing steadily in one direction; and in these 

 15 to 17 "steps" it will have moved over 20 to 25 mm. of surface. 

 But it frequently happens that the proboscis does not secure a firm 

 attachment, and, when the step is attempted, the proboscis slides 

 back to the foot and the body is not advanced at all. The proboscis 

 is then raised and waved about, another "step" is attempted, and 

 generally succeeds. The animal may thus move forward in a 

 straight line or it may take quite an erratic course. The shell 

 sometimes rests upon the operculum, sometimes it is simply dragged 



