ANATOMY OF ACLESIA FREERI. 67 



and all adults ; while the character of the body wall is such that 

 the internal organs are completely exposed by a few cuts with 

 the scissors. By using a hypodermic injection of cocaine and 

 atropine the animals can be killed fully extended. They are well 

 preserved by either alcohol or formalin. It has been found, 

 however, that the albumen gland must be well hardened, or it 

 will swell and break down into a gelatinous substance. The 

 dissection of aclesia is not without its difficulties, but this aclesia 

 is, in the opinion of the author, the best gasteropod form for 

 general class work with which he is acquainted. 



When crawling upon the bottom, even in clear shallow water, 

 these mollusks are not conspicuous, although easily distinguished 

 and followed when once found by the eye. Their colors blend 

 well with the sandy bottom, rendering them much less con- 

 spicuous objects than one would think from observing the 

 animals in an aquarium, where color and form show to the 

 greatest advantage. There is considerable variation in size 

 among the specimens collected, but the average is about 15 cen- 

 timeters long, 7 centimeters wide, and 5 centimeters high. The 

 posterior extremity extends some distance back of the visceral 

 mass, forming a broad, pointed tail. The creeping sole extends 

 to the tip of this part. The sides of the foot extend beyond 

 the margins of the body. 



The highest point of the body is at the level of the anterior 

 end of the branchial fissure. The slope from here to the head is 

 even and gradual, but abrupt and steep to the tail. 



The dorsal surface of the head and neck is considerably flat- 

 tened. The head is distinctly separated from the foot (fig. 10, 

 Plate III), but there is no dorsal or lateral demarcation between 

 the head and the broad, thick, neck region. The lips, which 

 inclose the large ventral mouth, are white in color, thick, and 

 creased. They form a flattened area of considerable extent 

 which is applied to the surface on which the animal is creeping. 

 At each side of the mouth, the head is produced into a pair of 

 large oral lobes, almost directly beneath the tentacles. The 

 ventral edge of the oral lobe is formed by an extension of the lip. 

 The tentacles arise from the latero-anterior angles of the head ; 

 they are long and large, tapering little from base to tip. The 

 auriculate tip is directed somewhat posteriorly, and extends in 

 the form of a small fissure down the posterior surface of the 

 tentacle about two-fifths of its length. When the aclesias move 

 about, the flattened surface of the tentacle is spread on the bottom 

 like the palm of a hand. The rhinophores are about as long as 



