1891.] Mr Groom, On the Orientation of Sacculina. 161 



definitely recognisable in the larva) but forming a membrane in 

 Sacculina running from the peduncle to the mantle-opening and 

 termed by Delage the mesentery. Symmetrically situated on each 

 side of the median plane are the oviducts opening into the mantle- 

 cavity by the two female genital pores*. The relation of the 

 oviduct to the ovaries is similar in both cases, though in conse- 

 quence of the different situation of the ovaries (due perhaps to 

 the special mode of nutrition in Sacculina) the relative lengths 

 are very different : in both, the lower part of the oviduct is 

 expanded to form a chamber 2 , the glandular walls of which, 

 simple in Lepas, but branched in Sacculina, constitute the 

 Kittdrilsen of the Germans and "Glandes cementaires" of Delage 

 (as Giard 3 has pointed, out and Delage admits, these glands have 

 no relation with the cement-glands proper of Cirripedia). The 

 function of these glands in both groups is to produce the peculiar 

 sac or cocoon 4 in which the ova are enclosed when lying in the 

 mantle-cavity as the ovigerous lamellae of Darwin 5 . 



The openings of the vasa deferentia (also symmetrical) in 

 Cirripedes are less constant in position than the other organs 

 mentioned, and I wish to reserve all mention of them for a future 

 occasion. 



The last structure to be compared in the two forms is the 

 nervous system. This in Lepads consists of a supra-oesophageal, 

 a large sub-cesophageal and a series of posterior ganglia. In Sac- 

 culina a single ganglion is present, corresponding probably in 

 position with the sub-cesophageal ganglia of Lepads or Balanids, 

 both being near the female genital apertures. 



Now both Kossmann and Delage are agreed that the plane of 

 symmetry passing through the mesentery in Sacculina is the 

 median vertical plane. Kossmann places the peduncle in front, 

 the mantle-opening behind and the mesentery on the dorsal line. 

 Delage making the mesentery ventral and the mantle-opening 

 posterior gives Saccidina a position diametrically opposite to that 

 of Kossmann. He bases his view solely on the situation and 

 origin of the ganglion. Since, he argues, this arises on the ventral 

 side in articulate animals, the neighbourhood of the edge of the 

 mesentery close to which the ganglion originates must also in 

 Sacculina be ventral ; in other words the mesentery is ventral ; 

 and since the nervous centre in Cirripedes is situated in the 

 region of the thorax, the ganglion of Sacculina must indicate the 



1 Krohn, Wiegmann's ArcMv. f. Naturc/eschichte, 1859. Hoek, Challenger 

 Report, Vol. x., Cirripedia, Anatomical Part, 1884. Nussbaum, loc. cit. 



2 Hoek, Nussbaum, loc. cit. 



3 Sur l'orientation de Sacculina Carcini. Comptes Rendus, 102. 



4 Hoek, Nussbaum, loc. cit. 



5 A monograph of the Cirripedia, Lepadidae and Balanidae, Eay Society, 1851, 

 1854. 



