356 PV. S. NICKERSON. [Vol. XVII. 



regularity in a single row, extending from a short distance 

 above the margin of the foot to a region behind the intestine, 

 where the peculiarities gradually become less marked and the 

 cells become indistinguishable from those about them. The 

 character of the cells is shown in PI. XXXII, Figs. 7 and 8. 

 The nuclei are large, rounded, and near the basal ends. A 

 narrow marginal zone of the cytoplasm is clear and free from 

 granules, and stains very faintly. The remaining portion is 

 filled with fine granules which stain so deeply with iron-haema- 

 toxylin as to make the body of the cell appear almost black. 

 The cuticula covering these cells seems to be in no way differ- 

 ent from that of adjoining regions. Concerning the function 

 of the cells I have little to offer. The character of the con- 

 tents would seem to indicate a secretory or glandular function, 

 though no conditions have been observed which point to a dis- 

 charge of the contents ; neither does there appear to be any 

 avenue provided for the discharge of the secretion. A row of 

 similar cells was described and figured by Salensky ('77) for 

 L. crassicauda and L. tethyae ; he considered them gland cells. 

 Harmer ('85) failed to find them in the specimens which he 

 studied. 



The structure known as foot-gland in several other species 

 is lacking in L. Davenporti. Neither in the adult nor in the 

 developing bud is any trace of it to be seen. Its place is 

 probably taken functionally by certain unicellular glands, from 

 twenty-five to thirty in number, distributed chiefly around the 

 margin of the foot (PI. XXXII, Fig. 15). They open by a 

 sort of bordered pit (PI. XXXIII, Fig. 34), which resembles a 

 minute sucker, with which Kowalevsky compared the corre- 

 sponding structures in L. Neapolitanum. They resemble very 

 closely the cells which he figured, the chief difference being that 

 in the American species a greater number is present. Around 

 the margin of the foot these cells are often grouped in clusters 

 of two or three, which may in some cases open by a common 

 pore. Those farther from the margin are more scattered and 

 open singly. These gland cells arise in the bud by the elonga- 

 tion and differentiation of certain cells of the body-wall in the 

 region which will become the margin of the foot when the 



