8 
CLASSIFICATION. 
6. — Gill or Ctenidlum of Viviparay a 
Peclinil.jranchiate Gastropod (after Lankester). 
/. intestine running parallel to axis of gill and end- 
ing in the anus a, ; br. rows of elongate branchial 
filaments. 
the coinpuiieiit parts of several of tlie i)aire(l organs, tlius tlie 
original left gill and other organs have become atrophieil, but the 
right gill, etc., retained, though owing to the rotatory move- 
ment the viscera have been subjected to, these originally de.xtrally 
placed organs are now i)laced to the left of the rectum. The Azygo- 
branchia may be separated into two sections : Pulmonata and 
PuCTiNiiuiANCiiiATA, containing 
the animals breathing air and 
water respectively, the former 
composed of those species which 
have become modified and 
adapted to a terrestrial life 
and aerial respiration termed 
Pneumonochlamyda by Lan- 
kester, and Xenrobranchiata 
by Macalister, of which Ci/clo- 
xtomd ('/('(/((IIS is ail e.xample ; while the Pectiiiibranchiata embrace 
all the operculate aquatic species. 
The Euthyueurous Gastropods 
comprise two Sub-orders, based up- 
on the position and function of the 
respiratory organs, viz. : Pulmonata 
and Opistiiobranchiata ; of the 
latter group the marine genus Build 
is an e.xample, and the Eiitliyneiir- 
ous Piilmonates comprise the bulk 
of our native lanil and freshwater 
molliisks. Though I have classed 
together the Euthyueurous air- 
breathers as simply Pulmonata, it 
should be mentioned that some 
Biologists do not regard the pul- 
monary sac of the Helicidcc as 
homologous with that of the Lim- 
nd/kliv ; the respiratory cavity in 
the former being said to be a modifi- 
cation of the cloaca of the kidney, 
hence the term Xepiiropneusta applied to them ; while that of the 
- vx. . ' 
Fig. 7. — Diagram of the Lung of a 
Pulmonate Gastropod, Ilelix aspcrsa L. 
nephridium, with ureter crossing its sur- 
face ; r. rectum ; a. auricle; z/. ventricle ; 
b.b. canal bringing blood from hinder part of 
Ijody ; c.r. canal communicating with body 
cavitj-and also bringing blood to lung. The 
darker veins carry the blood from these 
canals to surface of lung ; the light veins re- 
collect and convey to auricle after aeration. 
