REPORT ON THE PTEROPODA. 
39 
situated the acetabuliferous appendages, and I wish to lay special stress on the fact that 
they originate on the proboscis and have no connection with the foot. The form of these 
appendages varies in different genera, as was shown in the systematic Report on the 
Gymnosomata. In the different known species of Pneumonodermatidae these appendages 
have attained different degrees of development, varying from the condition in which the 
suckers are directly inserted on the proboscis ( Dexiobranchaea simplex ) to that in which 
they are carried on two long symmetrical stems ( Spongiobranclisea and Pneumonoderma). 
The structure of these suckers has been studied by Niemiec, 1 and by myself ; it differs 
essentially from that of the suckers of Cephalopods, also studied by Colasanti, 2 by Niemiec, 
and by Paul Girod. 3 
At the posterior end of the proboscis is the buccal mass, in such a manner that it is 
carried quite forwards, along with the horny pieces which it encloses, when the proboscis 
is evaginated. 
In this buccal mass (PI. IV. fig. G) are contained, as we have seen, two jaws united in the 
middle line (6), a powerful radula (c), and the organs known under the name of hook-sacs; 
these last are also seen of all degrees of development in the Pneumonodermatidae, from 
Dexiobranchaea where they form only two small depressions enclosing short hooks (a), to 
Pneumonoderma where they form long evaginable sacs (a') with a. wall covered with hooks. 4 
From the fact that the proboscis is evaginable, it follows that when it is expanded 
it must contain the anterior part of the oesophagus doubled up within it ; this latter then 
must increase in length with the proboscis, always being longer than it. The oesophagus 
is rather extensible and ciliated throughout its whole length as in other Pteropods. It 
is rather short and traverses a membranous diaphragm like that which we have seen in 
the Thecosomata ( Cuvierina , &c.), and which we shall also find in all the Gymnosomata. 
This diaphragm divides the general body-cavity into a cephalic portion, enclosing the 
buccal mass, the central nervous system, the penis, &c., and a posterior visceral portion. 
The oesophagus, in its passage through this diaphragm, is accompanied by the salivary 
glands, which open in the usual position, are much elongated, and do not present a marked 
separation between the secreting and conducting portions. They have been figured by 
van Beneden 5 as united by their posterior parts. I have always found, however, both in 
the various species of Pneumonoderma which I have examined, and in other genera, that 
the two salivary glands are free and distinct throughout their whole extent. 
The stomach forms a large pouch, with slightly muscular walls, entirely surrounded 
by the liver, which pours its secretion into it by numerous apertures ; this arrangement 
is observed in all Gymnosomata. 
1 Recherches morphologiques sur les ventouses dans le regne animal, Recueil Zool. Suisse, t. ii. 1885. 
2 Ricerche anatomicbe e fisiologiche sopra il braccio dei Cefalopodi, Atti R. Accad. d. Lined, ser. 2, t. iii.pt. 2, 1876. 
3 Recherches sur la peau des Cepholopodes, Arch, de Zool. JExpdr., ser. 2, t. ii., 1884. 
4 Compare the Systematic Report on the Gymnosomata, Zool. Chall. Exp., part Iviii. fig. 1, p. 6, 1. 
4 Recherches anatomiques sur le Pneumodermon violaceum, d’Orb., Mem. Acad. Sci. Bruxelles, t. xi. pi. i. figs. 4, 9. 
