On the Salivai'y and Mouth Glands of the Nudibranchiata. 141 
Secretory cells of the mouth glands are very diverse in histological 
structure ; they sit on the tubes or reservoirs either singly (Spurilla and 
Doto) or in groups of three or four (Facelma). They are always enveloped 
in a delicate connective tissue sheath the nuclei of which can be seen in 
Fig. II. and Fig. VI. 1. A comparison of Figs. lY. and VI. will show the 
absolutely different structure of the glands. The cells of Facelina can be 
described as follows : Nucleus large, poor in chromatin, rich in nuclear 
fluid, with large paranucleus ; protoplasm with numerous deeply staining 
(iron-hsematoxylin) spherical secretory globules which are seen to escape 
as minute drops into the lumen of the tube on which the cells sit ; a 
Fig. II. 
portion of the protoplasm (Fig. IV.) near the base of the cells is free of 
globules. Fig. III. shows a group of cells (1 and 2) in active secretion, 
and another (3) apparently recuperating after a period of secretion. 
The secretory cells of the mouth glands of Doto are remarkable in 
many ways. They are of enormous size, having diameters of up to '4 mm. 
The nuclei are also enormous (Fig. VI. 2) ; they have a number of large 
karyosomes but no nucleoli. The protoplasm shows an unusual structure ; 
there are two layers having a regular fibrillar structure — one layer 
immediately around the nuclear membrane and a peripheral layer ; in 
cell 2 of Fig. VI. these two fibrillar layers are seen to be continuous at 
the point where the secretion is discharged from the cell. In cell 4 of the 
