612 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



the local authorities my appreciation of the courtesies extended to me 

 during this time. 



1. The Integument. 



The integument consists of an outer epidermal layer, the cells of 

 which vary much in appearance, and a dermal layer of loosely united 



-a 

 a- 



FiGURE 2. Spicules of the foot, aa.bb., lateral margins of foot, 

 lucida, one inch ocular, and one-sixth inch objective. X 612. 



Camera 



connective-tissue cells. The epidermis is strongly ciliated on the sur- 

 face of the foot, and the cilia can be traced up the sides of the body, 

 although here they are much shorter ; the dorsum is entirely destitute 

 of cilia. The basal corpuscles at the base of the cilia are conspicuous. 

 The pigment of the integument is deposited in roundish vaculated 

 masses mostly at the inner ends of the epidermal cells. In the dorsum 

 the epidermal cells are broad, short, and highly vacuolated, but in 

 passing ventrally they gradually change to the elongated, cylindrical, 

 richly cytoplasmic cells of the foot. The cells in the epidermis of the 

 foot are fully twice as long as those on the back and are much crowded. 

 The glands of the foot are simple, flask-shaped, multicellular glands 

 having a small lumen. None of the epidermal cells of the foot appear 

 to be glandular, as are many of those on the sides and dorsum, and on 

 the rhinophores. The cells covering the gills constitute a thin colum- 

 nar epithelium of a simple character. Histologically the foot is dis- 

 tinguished by a thicker epidermis, numerous glands, and a larger 

 amount of connective tissue and irregularly shaped muscle cells. 

 The dermis contains numerous spicules, which vary in size from 15 



