071 the Salivary and Mouth Glands of the Nudihranchiata. 145 
which are large vacuoles which may have been filled with the secretion. 
The whole structure is enveloped in connective tissue which can be seen 
as a delicate membrane around the contracted secretory cells. 
The tubes of Calma are very similar to those of Facelina ; those of 
Berghia resemble to some extent those of Spurilla. 
The structure of the alveoli of Doto is quite distinct. The whole organ 
is again enveloped in connective tissue, nuclei of which can be seen at the 
points marked 1 in Fig. VI. Each alveolus is composed of a single layer 
of epithelial cells, each of which has a fair-sized nucleus and a coarsely 
reticulated protoplasm ; the dividing cell walls are wavy in section which 
is due to the points of attachment of the reticulum drawing the walls now 
this way then the other. The cells in the neighbourhood of a secretory 
neck are small and stain darkly, whereas those further off are fairly large 
(ten or more times as large as former) and only the nuclei and reticulum 
are deeply stained. 
3 
Fig. VI. 
10 
