THE GASTROPODA 131 
eggs in the water it surrounds them with a gelatinous mass, like 
the basommatophorous Pulmonates. 
In the ovoviviparous Gastropoda the progeny are born living 
after undergoing their development within the parent. They 
develop in the terminal portion of the oviduct in the following 
Streptoneura: Paludina, Typhobia; various species of Melania 
(Fig. 109), Littorina, Cymba, Janthina, Nassopsis, and the Entocon- 
chidae ; in the Opisthobranch Halopsyche ; and in numerous Pul- 
monates—viz. Glandina algira, Rhytida aequalis, Selenites voyanus, 
Helix rupestris, H. inversicolor, H. inaequalis, H. unidentata, H. 
erroned, H, studeriana, Patula cooperi, Acanthinula harpa, the genera 
Partula, Balea, Coeliaxis, Pupa muscorum, P. umbilicata, P. cylindracea, 
Clausilia ventricosa, C. similis, Achatina alabaster, and A. zebra, 
Stenogyra mamnillata (Fig. 8), S. octona, S. terebraster, S. domini- 
ciensis, S. decollata, S. lamellata, Ferussacia folliculus, F. lamellifera, 
Fia. 109. 
Melania episcopalis, out of its shell, showing the female genital SDATAUES, right-side view. 
@, anus; 0.0, brood-pouch opening ; b. Ps brood- -pouch ; f, foot ; 3 9-97, genital ciliated groove ; 
g.0, genital orifice ; m, mouth ; oc, eye; od, oviduct; op, operculum; ov, ovary. (After Moore.) 
F. procerula, F. debilis, Vaginula vivipara. The embryos develop in 
a special incubatory pouch excavated in the interior of the foot 
and connected with the extremity of the ciliated canal which passes 
from the female orifice to the head in Melania episcopalis (Fig. 109, 
b.p.) and Tanganyicia rufofilosa (Fig. 78, b.p). 
In viviparous Gastropods the ovum contains but little yolk, 
but in other forms the quantity of deutoplasm is greater, and is 
especially large in a number of Rachiglossa, such as Nassa, ete. 
The segmentation of the ovum is always total, and, except in cases 
in which the deutoplasm is scanty (Paludina), it soon becomes 
irregular. As a rule in Aspidobranchia, Taenioglossa, and Pul- 
monata, the two first cleavage planes are meridional, the first 
separating the right and left halves of the future animal. The 
third cleavage is equatorial and cuts off the micromeres at the 
animal pole from the macromeres at the opposite pole, so that, as 
a rule, there are four macromeres from the beginning (Fig. 9, A, B). 
These macromeres give rise to two more generations of micro- or 
