38 Moll. 
MOLLUSCA. 
is discussed in its bearings on classification, and tbe following arrange- 
ment proposed : — 
f i. Notoneur^s. 
“ 1°. Astrepsineur&s. 
1 
“ 2°. Strepsineur^s. | 
II. Gastroneur^s. 
in. Pleuroneurds. 
iv. Aponotoneurds. 
v. Epipodoneur^s.” 
Lacaze-Duthiers (1). 
Criticisms of Lacaze-Duthiers ; Pelseneer (8, 10, 11). 
Orthoneura proper do not exist. Orthoneury is a specialized cliiasto- 
neury; Pelseneer (5). 
From an exhaustive examination of the nervous system, it is concluded 
that the arms of the Cephalopoda are pedal in origiu, and hence not 
homologous with the buccal appendages of the Pteropoda gymnosomata ; 
Pelseneer, (2) pp. 65-74 ; also id. (4). 
Bouvier’s conclusions regarding the nervous system of Valvata are 
substantiated ; Garnault (4, 6) : these are criticised ; Bernard (2). 
In the suboesophageal nervous mass of Fissurella two centres are mor- 
phologically distinct, quite as much so below as above ; the study of 
early embryos confirms this. The ganglia have the form of cylinders, 
united in pairs by one of their faces. The collarette is a part of the 
mantle, and may be termed “ inferior mantle Boutan (2). 
Curvilinear motion towards the injured side in Snails, whose supra- 
oesophageal ganglia have been destroyed, is described ; Petit. 
The pedal nerve-cords of Trochus and other genera are described ; 
they are single, not double as stated by Lacaze-Duthiers. The epipodium 
of various Gastropods is discussed, and its true pedal nature and homo- 
logy with the funnel of Cephalopods maintained ; Pelseneer (6, 7). 
The minute distribution of the nerve-endings in the digestive tract of 
Helix described ; Grieb. 
Influence of the nervous system on ciliary motion ; Vvedenskii. 
8 . Sensory Organs . 
In Prosobranchiata the neurilemma of the optic nerve expands into a 
transparent basal membrane ; the pigment is external to the layer of 
rods. The unpigmented, flask-shaped cells gradually diminish at their 
outer ends, and pass into nerve-fibres, as first made out in Ptero- 
trachea. The rods consist of delicate columns, rounded internally, 
longest near the fundus. The connective framework of Simroth 
contains stellate cells as well as fibres. Structure of the vitreous 
body elucidated. In Pecten all parts of the Gastropod eye are present ; 
Kalide (2). 
Sense-organs of the mantle-margin of the Ostreacea treated in great 
detail ; Rawitz (2). 
In the rudimentary eyes of Guivillea the refractive media and pig- 
ment have disappeared ; the retina has lost its cellular elements, and the 
optic nerve its fibrillar structure. An account is also given of the rudi- 
mentary nature and absence of the eyes of various other Mollusca , and 
animals dwelling in caves ; Pelseneer (3). 
