CEMENTING APPARATUS. 147 



suspended had become, as viewed from the outside, deeply 

 concave — the cement had apparently continued to try to 

 reach the rock, and now hung down in the form of two 

 thickish roots, some tenths of an inch in length. These 

 roots were round, and tapered either to a fine or blunt 

 point ; one was doubled on itself, and so had become united j 

 in the other, I could perceive five layers or sheaths of the 

 cement-tissue, one within the other ; the innermost of these 

 layers, which once, no doubt, formed the outside surface of 

 the root, was only a quarter of its present length. 



In Bala?ius tintinnabulum, the basis is calcareous : when 

 its upper surface is cleaned, dried, and examined under a 

 good light, the numerous larger cement-ducts can be 

 seen, even by the naked eye, or under a weak lens, and 

 present an elegant appearance. These larger ducts run in 

 parallel lines from the two chains of glands towards the 

 circumference. They are all encrusted with calcareous 

 matter, and in the more central parts are hidden under it ; 

 at each period of growth, when the basis is added to round 

 the circumference, it would appear that a layer of excessive 

 tenuity of shell is thrown clown over the whole surface, just 

 in the same way as in Tubicinella, at each period, a new 

 and larger disc of membrane was thrown down over the 

 pre-existing membranes with their cementing apparatus. 

 The cement-glands, in the middle of the basal plate, seem 

 often to give rise to small abnormal depositions of calca- 

 reous matter. When the basis (it is best to take a young 

 specimen) is slowly dissolved in acid, all the cementing 

 apparatus is left uninjured, adhering to the delicate tissue 

 which before existed in a calcified condition. Near the 

 middle I saw the two antennae of the pupa; and from 

 them the two cement-trunks extended about half-way 

 towards the circumference. These two chains of glands are 

 often placed very irregularly, but they tend to form, as in 

 Coronula, a large angle, open towards the rostral end of the 

 shell. The glands, close to the old antennae, commence 

 abruptly, of rather large size : the later-formed glands, with 

 their ducts, are in regular order larger than the younger ones, 

 and stand much closer together. After immersion in acid 

 all the glands and ducts appeared empty, instead of the older 



