THE AMPHINEURA 59 
gastric commissure is given off from the cerebral mass, and enters 
a pair of small ganglia situated in the median line between the 
oesophagus and the radular sac; moreover, the two same upper 
buccal and subradular commissures as in the Chitones are present, 
at least in Proneomenia and Rhopalomenia (Heath). 
The only organs of special sense are the club-shaped epithelial 
papillae in the thickened cuticule of the Proneomeniidae, Neomenia, 
and the following Parameniidae, Dinomenia, Proparamenia, and 
Paramenia. There is also a median invaginable sensory papilla 
situated on the dorsal posterior surface, above the rectum. It is 
not covered by the cuticle, and may be multiple, as in Dondersia, 
or absent, as in Hemimenia and perhaps Strophomeniua. 
Generative Organs. —The Neomeniomorpha are hermaphrodite. 
The gonads are paired tubular structures, separately opening 
posteriorly into the pericardium (Fig. 30, C) and extending forward 
close under the dorsal sinus to near the front end of the body. The 
ova are developed on the median, the spermatozoa on the outer 
wall of each gonad. The sexual products pass into the pericardium, 
whence they are driven by the pericardial cilia into the kidneys, 
which, as has been explained above, serve as gonaducts and are 
provided with receptacula seminis and shell-glands. In several 
species paired excitatory organs, in the form of protrusible cal- 
careous spicules, are situated in the cloacal chamber on either 
side of the uro-genital orifice. 
Ill. Empryo.oey. 
Little is known of the development of the group. The ova are 
laid separately. In Myzomenia banyulensis (Pruvot) 
the segmentation is regular, and an invaginate 
gastrula with an originally posterior blastopore is 
formed. An anterior ciliated ring or velum is 
formed, having in its middle a tuft of cilia, which 
is eventually transformed into a single terminal 
flagellum (Fig. 17). The external surface of the 
trochophore larva thus formed is made up of a 
number of ciliated test-cells, which—as in the 
Lamellibranchiate Yoldia—eventually are cast off 
and the mantle is formed beneath. The post- . |, 
3 : n advanced larva 
velar region of the embryo elongates, and its of Myzomenia banyu- 
ectoderm cells develop spicules. Finally, the (0° ante’ oven 
velum disappears, and seven imbricated calear- is (ulsn ol (After 
eous plates, made up of more or less flattened, 
closely-apposed spicules, are formed on the dorsal surface 
(Fig. 39). 
My 
Fic. 39. 
