The anatomy of Lucapina crenulata. 



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tracted so that almost the whole shell is exposed. The mantle covers 

 almost the whole animal, coming down close on the sides of the foot 

 when contracted. Its external coat is black and quite smooth, the 

 rough appearance in contracted specimens being caused by the folds 

 of the pigmented epitheHum. The under side is light colored and also 

 very smooth. At the margin of the shell, the tissue is particularly 

 vascular, and the shell matrix shows a series of indentations, into 

 which the little projections of the shell fit. The whole mantle is very 

 spongy, little streams of water jetting out when a slight pressure is 

 applied. While at the Hopkins Seaside Laboratory I had an excellent 

 opportunity to study the movements of the living animals. The anterior 

 part of the mantle was often thrown up and back while the animals 

 were moving about. This gave a freer access to the light, and the 

 ctenidia were exposed for about one-half their length. Evidently this 

 part of the mantle is much more sensitive than other regions, and we 

 shall see a reason for it when we examine the nerves. 



Fig. D. Median cross-section of Lucapina (posterior view, ideal section). Ep epi- 

 podium, F foot, Lp. a lateral pedal artery, 31 mantle, P. a pedal artery, Pal. a palliai 

 artery, P. P. con iiallio-i^leural connective, P. s palliai sinus, S i^osition of shell, Cp.Ch 

 circumpallial chord or mantle ring nerve. Vis visceral cavity, c epipodial nerve. 



The epipodium in Lucapina is very rudimentary, and scarcely 

 shows at all in some individuals. In a contracted specimen, however, 

 there will be seen a slightly protruding papillate ridge, about midway 

 between the attachment of the mantle and the lower surface of the 

 foot (Fig. D Ep). It is more prominent on the sides than anywhere 

 else. We shall see by tracing the nerves that this is undoubtedly a 

 rudimentary epipodium. 



The foot is a broad, flat oval surface (Fig. C), well supplied with 

 mucous glands, which enable the animal to adhere very closely to the 



