ia General Morphology. 



considerably, but it must be remembered that the dorsal fold in Cirripedes which cuts off the 

 body from the mantle is developmentally a late modification , the Cypris larva possessing a 

 median dorsal attachment of the bivalve carapace to the body, which. we may take to represent 

 the mesentery of Peltogaster. Obliterating therefore the fold along the dorsal middle line in 

 our typical Cirripede and apposing the posterior edge of the mantle towards the head so as to 

 form a small anterior mantle opening, we obtain the essential relations of Peltogaster in ali 

 respects. This morphological comparison, which was suggested to me by Dr. Calman, appears 

 so satisfactory that on the strength of it we may proceed to fix the orientation of Pelto- 

 gaster, and by implication of the Khizocephala in general. 



Clearly the long axis of the mesentery fixes the antero-posterior axis, and the anterior 

 pole is occupied by the mantle opening. The mesentery is situated onthe dorsal sur fa ce, and 

 the ring of attachment is homologous to the stalk orpeduncle of the Cirripedes. 

 The ganglion, situated anteriorly and dorsally, corresponds to the brain of the Cirripedia. 



The morphological interpretation here offered is different to that of Delage (14, p. (599 

 and 700), who relying on the fact that a single ganglion is present, considers that the body 

 of the Khizocephala represents merely the head of a normal Cirripede , and since the ganglion of 

 Sacculina is developed from a portion of the mantle and the visceral mass near the mesentery, 

 he regards the mesenterial surface as ventral, because the nervous system is always developed 

 ventrally in Crustacea. But we may object that the ganglion is developed laterally and not 

 in the line of the mesentery (see p. 53), and in answer to the first proposition we know that 

 the nervous system of the males of Scalpellimi, whose bodies certainly represent the whole 

 body of a Cirripede, is reduced to a supraoesophageal ganglion and a single thoracic ganglion: 

 I am therefore not inclined to sacrifice the general comparison of the body of the Rhizo- 

 cephala to that of an ordinary Cirripede for the reasons urged by Delage. 



Definite connecting links between the Rhizocephala and the other orders of Cirripedia 

 have not been hitherto shown, in my opinion, to exist: though Giard (21) contends that the 

 parasite Sphaerothyìacus, described by Sluiter (Uber einen in Ascidien schmarotzenden Wurzel- 

 krebs. in: Nat. Tijd. Nederl. Indie Batavia Deel 43) from the gill of a Cynthiad Ascidian, is an 

 intermediate form between the Ascothoracica and Rhizocephala. The presence in this animai 

 of a well developed gut and its infection of an Ascidian, both of which characters are utterly 

 unknown among Rhizocephala, may make us sceptical in accepting this little known genus as 

 a connecting link, but it is at least interesting to perceive how the whole Cirripede body can 

 be represented by an ovai sac without limbs or sense organs as the result of a parasitic 

 mode of life. 



Another genus which has been suggested as belonging to the primitive Rhizocephala 

 is Sarcotaces, described by Hjort (Zur Anatomie und Entwicklungsgeschichte einer im Fleisch 

 von Fischen schmarotzenden Crustacée. in: Vid. Selsk. Skrifter Christiania 1 895), but here again 

 the presence of a gut, the nature of the host, and the imperfect characterisation of the animai, 

 precludes our acceptance of it at present. 



