138 BALANID.E. 



formed slips, new and larger laminae being all the time 

 thrown down, so as to prevent any fissure being formed. 

 I also suspect that the gradual increase in width of the 

 circumferential slip itself, is due to the opposed edges of 

 the underlying and last-formed circumferential slip being 

 dragged further apart from each other, new and wider 

 laminae of membrane being continually thrown down ; the 

 new circumferential slip being thus, also, all the time 

 thickened, as well as rendered broader. 



The central slip or rather disc of membrane, is ifgths of an 

 inch in diameter; and this shows the basal diameter of the 

 shell immediately after the metamorphosis. In the middle 

 of this little disc I saw, in several specimens, the prehensile, 

 pupal antennas ; I made out distinctly the ultimate segment 

 with its bristles, and, as I believe, the disc-segment, which 

 was rJooths of an inch in diameter ; but this portion was 

 much obscured by the quantity of cement. When the 

 corium is removed from the inner side of the basal mem- 

 brane, the two chains of glands, extending from exactly 

 over the antennae in the centre about half way towards the 

 circumference, are conspicuous. The cement-trunk, con- 

 necting the glands, is thin, and at the further end is always 

 broken off, by the removal of the corium and overlying 

 layer of ovarian caeca, into which the two cement-trunks 

 enter; and without which removal, nothing could be 

 seen. The two chains of glands form a very large angle, 

 open towards the rostral end of the shell, as represented 

 at fig. 1 c, much enlarged ; by a mistake in fg. 1 a, the 

 two have been drawn in a straight line. The cement-trunk 

 increases in diameter in proceeding from the centre to the 

 circumference, and the glands likewise increase in size, at 

 the same time altering somewhat in shape. From near 

 the lower side (the basal membrane being viewed from 

 within) of each gland, two cement-ducts proceed, which 

 pour out their contents beneath the basal membrane. The 

 orifices of the ducts always exactly face the middle folds of 

 the two lateral, and two carino-lateral compartments. In 

 a full-sized specimen, there are from thirty-five to forty 

 cement-glands on each side, always corresponding exactly 

 with the number of slips of basal membrane, including the 



