110 S. GOTO. 



the median line. The cells, especially of the ventral groufis, are far 

 removed from the ootyp ; and they are therefore provided with long 

 efferent ducts, which open into the ootyp after making more or 

 less windings on the way (PL XVI, fig. 4). In Tristomum also, the 

 shell-glands are far removed from the ootyp, and open by means of 

 long ducts into its very beginning (PL XXII, fig. 3). In some 

 species of this genus (e. g. Trist. sinuatuni) the wall of the ootyp sends 

 out a few small, tubular evaginations, into which the shell-glands open 

 (PL XXII, fig. 6). In Monocotyle too, these glands are provided with 

 long stalks, and open only at the beginning of the ootyp. 



As to the shell-glands themselves, they are in most species of an 

 irregular polygonal form. The nucleus is more or less vesicular and 

 contains one or a few nucleoli ; the protoplasm is usually granular, 

 stains well, and is wholly destitute of any external membrane. The 

 glands, however, often appear like small naked nuclei, owing to the 

 shrinkage of their protoplasm. This condition is evidently owing to 

 exhaustion, and corresponds to the period of complete rest. In Mono- 

 cotyle the shell-glands are eUipsoidal or spherical, and are, as ah-eady 

 stated, provided with long stalks (PL XVIII, fig. 1). The nucleus, 

 which contains in this case usually a single nucleolus, occupies a more 

 or less eccentric position, and the cytoplasm is finely granular and 

 stains Aveakly. The ducts are on the other hand often filled with a more 

 deeply staining, and more coarsely granular substance ; the cytoplasm 

 and the contents of the duct being sometimes separated by a sharp 

 line (PL XVIII, fig. 1). I do not know what interpretation to put on 

 this phenomenon, except to regard these goblet-shaped cells as having 

 arrived at the culminating point of their secretory activity and to have 

 almost entirely emptied themselves of the product of secretion, leaving 

 only the protoplasm in the body of the cell — in other words, I regard 

 the deeply staining contents of the duct as the product of secretion, and 



