354 IV. S. NICKERSON. [Vol. XVII. 



present, one is always larger than the other. Cross-sections of 

 tentacles are represented in Figs. 9 and 10. Each consists of a 

 single layer of epithelial cells surrounding a central core of the 

 gelatinous parenchyma, the cells on the inner or atrial side 

 being ciliated. Kowalevsky ('65) has described the tentacles 

 of L. Neapolitanum as having their anterior faces composed of 

 three rows of cells, definitely arranged, the middle row being 

 depressed to form a groove of which the two lateral rows 

 form the edges and bear cilia. No such definite arrangement 

 of cells is present in L. Davenporti, and the distribution of 

 cilia is uniform over the whole inner surface. Muscle fibers 

 have been described as extending into the tentacles, by Kowa- 

 levsky in L. Neapolitanum, and by Davenport ('93) in Urna- 

 tella. I have preparations of L. Davenporti stained by the 

 methylen-blue intra vitam method, which show two fibers, one 

 on each inner lateral face, extending into each tentacle and 

 there dividing into fine branches. These fibers I have not 

 observed either in sections or in entire preparations stained by 

 other methods. I have been unable positively to determine 

 whether the fibers in question are muscular or nervous in func- 

 tion, though I incline strongly to the latter view. The two 

 kinds of fibers are so intimately associated in the marginal por- 

 tion of the lophophore, and react so nearly alike to the methy- 

 len-blue stain, as to make it often extremely difficult to decide 

 in which class a particular fiber belongs. 



A thin fold of the epithelium, the velum, extends outward 

 from the margin of the lophophore, partially closing the atrial 

 aperture when the lophophore is contracted. It is attached to 

 the outer side of each tentacle, near its base, at which point a 

 little protuberance is formed (PI. XXXII, Fig. 3) which con- 

 tains a single peculiar large cell. In PI. XXXII, Fig. 10, is 

 shown the appearance of one of these cells, as seen in a cross- 

 section of the tentacle. The large, nearly spherical nucleus is 

 situated in the basal portion, while through the cytoplasm a 

 number of delicate lines extend perpendicularly toward the 

 surface. The cuticula over the cell is thickened to form a 

 flattened or sucker-shaped protuberance (Figs. 3 and 10). The 

 explanation of the function of these cells is furnished by a 



