CEMENTING APPARATUS. 149 



the circumferential duct, and the other (f) bifurcates again ; 

 of the latter, one branch unites with its fellow from the 

 opposite gland, and then forming a single duct (f) enters, 

 as do the two other branches, the circumferential duct. Thus, 

 into the latter, five main ducts enter: the position of their 

 points of entrance, with respect to the shell, varies consider- 

 ably ; but I think the five points tend to face the middle of 

 the rostrum, and middle of the two lateral compartments on 

 each side. In some other specimens, in which the ducts 

 were nearly as simple, I observed that the neck or main 

 duct at once divided into three branches, instead of into 

 two, with one soon bifurcating; and on one side a rudi- 

 mentary branch or spur was given off (above t), indicating 

 a tendency to an additional bifurcation. In the later- 

 formed glands, the ducts proceed only from the outer sides 

 and form the ends of the glands furthest from the centre ; 

 but in the earlier-formed and smaller glands of the same 

 individual, other ducts proceed from the inner sides, where 

 in the older glands the spurs (m) are situated : moreover, 

 in the younger glands, all the ducts bifurcate much oftener 

 (how often I was not able to ascertain), before entering the 

 circumferential duct; many of the branches, however, ter- 

 minating in spur-like points. Now if we imagine twenty 

 or thirty repetitions of the ducts given in fig. 4 a, (inde- 

 pendently of the greater complication of the ducts of the 

 younger glands), each a very little smaller than the other, 

 and placed, with the main branches parallel, one over and 

 within the other, we shall gain some insight into the won- 

 derfully complicated structure of the cementing apparatus 

 in this and many other species of Balanus. 



I have as yet only alluded to the circumferential duct 

 {i, i, PL 28, fig. 4<a): we have not hitherto met with this 

 duct, but I suspect that the branches which in Chelonobia 

 inosculate, and which seem to run nearly parallel to the 

 circumference of the basal membrane, answer the same 

 purpose of connecting the ducts together, and are, perhaps, 

 strictly homologous. In this, and some other species of 

 Balanus, the last-formed circumferential duct runs round 

 the margin of the upper lamina of the basal plate, close 

 to the basal edges of the walls ; and as these latter have 



