352 TEREBRATULIDiE. 



discs have remained adherent to them, when the shell 

 membranes were torn asunder ; and are seen edgeways, as 

 in fig. 3, «.* There can be no doubt, therefore, that these 

 membranous cceca occupied, in the living animal, the per- 

 forations already described as penetrating the shell from 

 one surface to the other. This will be still more evident 

 on reference to fig. 39 of my former report ; in which it 

 will be seen how exactly the shape of the caeca corresponds 

 with that of the perforations, when the latter are laid open 

 lengthways by a section of the shell perpendicular to its 

 surface. The lower margin of that figure corresponds with 

 the outer surface of the shell, and the diameter of the per- 

 forations is seen to be there greatly increased. With 

 regard to the office of these caeca, however, I am unable as 

 yet to give any distinct explanation. Their contents are of 

 a brown granular character, in which I have recognised 

 distinct cells (fig. 4), such as are to be met with in the 

 tubuli and follicles of ordinary glands ; and their whole 

 aspect satisfies me that they must be regarded as possess- 

 ing a glandular character. I have not been able, however, 

 to discover the nature or destination of their secretion. 

 The internal orifices of the perforations obviously consti- 

 tute the outlets of the caeca ; but there does not appear to 

 be any system of tubes or canals for collecting the matters 

 poured out from them, each caecum having its distinct and 

 independent termination on the internal surface of the 

 shell. Although the unusual degree of adhesion between 

 the mantle and the shells of Terebratula, first noticed by 

 Professor Owen, formerly led me to suspect that the 

 mantle might send prolongations into the perforations of 

 the shell, I have not been able to discover any vestige of 

 such. On the contrary, it has appeared to me that the 



* See plate in the work cited. 



