1908.] ASPIDOBRANCH GASTROPOD MOLLUSCS. 843 



■elaborate aiTangement is derived from a comparatively simple 

 mixed ciliated and glandular epithelium is very well shown in the 

 terminal chamber of the male ducts of Nerita (fig. 52). Precisely 

 tlie same fundamental structure is found in all the glands on the 

 course of the female ducts. In the ootype gland the cell-bodies are 

 coarsely granular and stain deeply in hjematoxylin, the granules 

 of secretum are highly eosinophilous, and the ciliated cells are 

 moderately long. In the " clear gland " the cj'toplasm of the 

 gland-cells is scarcely granular, is not stained appreciably by any 

 of the oxTlinary dyes, the " stalks " or ducts of the cells are 

 relatively large, their contents clear and unstained by reagents. 

 The ciliated cells are somewhat widely sjDaced, and conspicuous 

 because they are not hidden by granules in the secreting ducts 

 <fig. 27). 



In the " mucous gland " the bunches of glandular cells are 

 large ; the gland-cells are dark and granular and their cytoplasm 

 stains deeply with ha?matoxylin and picro-indigo-carmine. The 

 secretory granules are not so lai-ge as in the nterine gland, are 

 of unequal size, and as they are not eosinphilous, but stain blue 

 with picro-indigo-carmine and deeply with hasmatoxylin, they are 

 probably mucinogenous. The ciliated epithelial cells between 

 which the imicellular ducts run are very much elongated. 



In the '' rose-coloured gland *' the bunches of gland- cells are 

 rather small ; their cytoplasm stains rose-pink with picro-indigo- 

 carmine, carmine, or eosin ; they are not granular, and their 

 ducts contain a non-granular coagulum which is highly eosino- 

 philous. The ciliated cells are short. 



In the " vitelline gland " (fig. 28) the cell-bunches are of 

 moderate size ; the gland-cells have a reticular cytoplasm staining 

 faintly with picro-indigo-carmine or hsematoxylin ; the secretory 

 granules are small, of equal size, and faintly stained by the 

 reagents mentioned ; the ciliated cells forming the boundary 

 epithelium are cleai'ly defined and of moderate length. 



It is evident that, although it is not possible to attribute precise 

 functions to the different glands, they are to be regarded morpho- 

 logically as diflerentiations of a tract of mixed glandular and ciliated 

 epithelium, the histological characters of which are such that it is in 

 the highest degree probable that it has been formed as an invagi- 

 nation of the mantle-epithelium — that is to say, of the ectoderm. 

 The histology of the vagina, vaginal duct, sperm-sac, and ductus 

 enigmaticus is quite diflferent. These oi'gans are non-glandulai', 

 and are all lined by a very similar ciliated cubical epithelium, 

 which at first sight does seem to be very similar to the epithelium 

 of the oviduct, and different from that of the mantle-cavity. But 

 a careful examination with high powers of the microscope shows 

 that they are difierent. In the oviduct the cytojilasm of the cells 

 is differentiated to form a distinct refractive external border, the 

 cilia aae longer and stouter, the nuclei are moi'e elongated and 

 stain more intensely than is the case in the bursa copulatrix and 

 the ducts leading from it. Moreover, when the vaginal duct is 



