GENERAL NOTES ON MOLLUSCS. 4it 
female. There its discoverers described it’ as a parasitic worm, 
“* Hfectocotylus.” The lost arm is afterwards regenerated. In Sepia, 
however, the modified arm is not discharged, but is simply thrust into 
‘the mantle cavity of the female. The spermatophores probably enter 
the oviduct, and burst there. 
Fic, 221.—Bunch of Sefza eggs attached to plant.—After Jatta. 
The eggs, when laid, are enclosed within separate black capsules 
containing gelatinous stuff, but the stalks of the capsules are united, so 
that a bunch of ‘‘ sea-grapes ” results. 
GENERAL NoTEs on Mo.Luuscs 
From the description of these three types a general idea 
of the structure of Mollusca may be obtained, but it should 
be noted—(r) that all the three types are specialised ; (2) 
that two small classes, the Solenogastres and the Scaphopoda, 
are unrepresented in the descriptions; (3) that in the three 
classes to which the types belong there is much diversity 
of structure, this being especially true of the large and 
heterogeneous class of Gasteropods. 
In surveying the structure of the whole group, it is con- 
venient to begin with the most striking of the external 
characters—the absence or presence of a well-developed 
head region. 
In the Lamellibranchs or Pelecypoda the head is absent, 
and along with it the tentacles, the radula, and the 
