DESCRIPTION OF PLATES, 28, 29. 669 



Fig. 2, Cement-ducts and one cement-gland of Chelonobia patula, 

 represented without the basal membrane, to which they 

 adhere : f f 3 main cement-trunk ; g, enlarged portion ; 

 h, gland ; a, b, the two ducts proceeding from this gland, 

 and bifurcating several times before debouching on the 

 under side of the basal membrane. Several other cement- 

 ducts, proceeding from other glands, are represented just 

 as they appeared under the microscope. 



3, Cement-ducts and glands of Tubicinella trachealis, repre- 

 sented without the basal membrane to which they ad- 

 hered : (f) (y), main cement-trunk, connecting the several 

 glands ; h, cement-gland ; a, cement-duct, with a singular 

 loop (a') having two projections or rudimentary branches; 

 b, spur or rudiment of a second cement-duct; c, third 

 cement-duct. 



4 a, Chain of cement-glands of Balanus tintinnabulum, with all 

 the ducts removed, excepting those proceeding from the 

 last-formed gland, which latter correspond in age with the 

 last-formed zone of the shelly basis ; the whole of the basis 

 having been removed by acid. 

 f main cement-trunk connecting the glands. 

 gh, last-formed cement-gland. 



k, t, two cement-ducts, proceeding from a great common duct ; 



one of these bifurcates at (t), and one branch joins at (t 1 ) 



the corrresponding branch from the corresponding gland. 



i i i, circumferential duct, into which the ducts k, k, t, t, t' all 



enter. 

 i! i', branches proceeding from the circumferential duct, which 

 branch and sub-branch till they form a sheet (z z) of 

 cement-tissue on the outside of the basis of the shell. 



4 b, two cement-glands of Bal. tintinnabulum (this figure, to match 

 with 4 a, ought to have stood upside down), taken from 

 near the centre of the basis, greatly enlarged ; (ff), main 

 trunk; (g), enlarged portion of the trunk; (A), gland; k, t, 

 two cement-ducts proceeding from a common point, one of 

 them (t) bifurcates, and gives off a rudimentary branch, t' ; 

 m, a spur, or rudimentary duct. The gland, h, has been 

 pushed on one side, it ought to lie over the enlarged 

 portion (g). There is a considerable difference between 

 these two glands and that (g h) represented in fig. 4 a; the 

 neck of the gland in the latter bejng elongated into a great 

 common duct, and the spur or rudimentary duct (m) being 

 absent. 



PLATE 29. 



Cirri : Larva, first stage. 



Fig. 1, Sixth cirrus of Balanus amphitrite (var. cirratus), showing 

 the muscles. 

 («) (b), flexor and extensor muscles, moving the upper segment 

 (i to k) of the pedicel. 



