286 LECTURE XIII. 



formed one, now immediately to be moulted with the other integuments 

 of the body. As soon as this exuviation is effected, the tender ova, 

 united into two lamellae, and adhering as yet to the bottom of the sac, 

 are exposed : as the membranes harden, the lamellas become detached 

 from the bottom of the sac, but are prevented from being washed out 

 by becoming united to semicircular folds of skin continued from each 

 side of the point of attachment of the body to the sac. These folds, 

 or " fraena," usually large, but in Ibla minute, are formed of chitine 

 with underlying corium, and their free border is beset with minute 

 pedunculate or clavate glandular bodies, secreting an adhesive sub- 

 stance serving to unite the ovigerous lamellae to the fraena. In some 

 species of Pollicipes the fraenal folds are destitute of the glands, and 

 do not subserve the function allotted to them in other Lepadoids. 



Mr. Darwin, to whom we owe the above details, is of opinion that 

 the lamelliform gills of the Balanoids are the homologues of the 

 fraena. " The ova are impregnated (as I infer from the state of the 

 vesiculae seminales) when first brought into the sac ; and whilst the 

 membrane of the lamellae is very tender the long proboscidiform penis 

 seems well adapted for this end. In the male of Ibla Cummingii, which 

 has not a probosciformed penis, the whole flexible body, probably, 

 performs the function of the penis : in Scalpellum ornatum, however, 

 the spermatozoa must be brought in by the action of the cirri, or of the 

 currents produced by them. That cross impregnation may, and some- 

 times does take place, I infer from the singular case of an individual 

 in a group of Balani, in which the penis had been cut off, and had 

 healed without any perforation ; notwithstanding which fact, larvae 

 were included in the ova." 



Mr. Darwin has shown that the organ, by the secretion of which 

 the Cirripeds attach themselves to foreign bodies, is a modified part 

 of the ovarian tube. In the Lepadoids there are two cement-glands, 

 situated high up in the midst of the ovarian caeca, with one cement- 

 duct proceeding from each ; the cement issues from the prehensile 

 antennae, and in some cases, at a later period, it escapes through 

 apertures in the peduncle. In the Balanoids, at each period of 

 growth a pair of new cement-glands is developed, larger than those 

 last formed, and making, with the older glands, a chain connected 

 together by the cement-trunk. They all adhere to the basal mem- 

 brane or the basal shelly plate. 



The supplemental male of the Scalpellum vulgare (fig. 125) is 

 found attached over the fold in the occludent margin of the scutum 

 of the large hermaphrodite individual ; and is sometimes imbedded 

 more than half its length in the spinigerous chitine. It is an ovate, 

 compressed, flask-like body, having a fimbriated orifice (a) at one 



