10 Moll. 
MOLLUSCA. 
In the heart of Pecten and Anodonta, Helix and Aplysia^ J. Dogiel 
has found transversely striated muscular cells, and in the wall of the 
atrium, what he calls apolar ganglious cells ; Arch. mikr. Anat. xiv. 
pp. 69-65, 1 pi. Foster and Dew-Smith, on the contrary, deny the 
presence of nerves and ganglia within the heart of Mollusks ; tom. cit. 
pp. 317-321. 
H. V. IiiERiNG distinguishes in the gills of bivalves two primary and 
two secondary plates — the former attached immediately to the trunk and 
without transverse connections, the latter to the free ventral edge of the 
former. The primary alone are to be found in the NucuUdce and 
Solemya ; only one secondary, the inner, is to be seen in Anatina and 
Lucina ; the outer secondary blade is much lengthened in Cyrena and 
many Tellinidce. Z. wiss. Zool. xxix. p. 610. 
A. Sabatier describes the transverse connections between the longi- 
tudinal rays in the gills of Mytilus eduUs as distinct hyaline bodies of 
high refraction, which he calls ‘ ‘ disques interm^diares,” and which, 
according to him, exhibit rhythmical expansion and contraction about 
seventy times in a minute, assisting in the circulation of water within 
the gills. Ann. Sci. Nat. v. No. 1. 
According to R. Bonnet, all capillaries in the gills of Bivalves are 
true vessels, provided with a distinct endothelial membrane in Mytilus 
edulis ; the same is the case in Area and Pinna, but in these they are 
interrupted in some spots by reticulated sponge-like lacunse. In fresh- 
water Bivalves, no endothelium could be found in the gill-vessels. As to 
the structure of the framework of the gills, the author adopts the three 
types proposed by Alder and Hancock — (1) thread-like gills in Mytilus, 
Area, and P Anomia ; (2) perforated gills in Mya, Pholas, Anodonta, and 
Unio ; (3) plaited gills in Ostrea, Cardium, and Pinna ; and adds (4) 
gutter- or groove-shaped gills, consisting of separate plaits without trans- 
verse anastomoses, in Pecten jacobceus. Morph. JB.j iii. pp. 283-327, 
with 3 pis. 
0. Posner (1. c.) agrees with the former in regarding the filaments in 
the gills of Mytilus as morphologically identical with the rays \n Ano- 
donta, but admitting the filaments in Pecten as of a higher degree of 
composition, corresponding each to about twenty filaments in Mytilus or 
rays in Anodonta, and to the secondary plaits in Ostrea. Arch. mikr. 
Anat. xiv. pp. 132-157, with 1 pi. 
The arrangement of the vibratile epithelial cells in the gills of Bivalves 
is accurately described by 0. Rabl, Jen. Z. Nat. xi. pp. 349-364, with 1 
pi., and by O. Posner, 1. c. 
The structure of the gills in Mytilus, Dreissena, Anodonta, Area, and 
Some other genera, has been examined by J. H. Peck. In Mytilus 
and Area, the longitudinal rays are transversely connected only by 
over-lapping fascicles of cilia, “ciliated interfilamentary junctions,” 
and this is to be regarded as a lower form. In Anodonta, true inter- 
lamellar junctions by fibrous masses, and remarkable in the relative 
strength of the correspoudent parts in the outer and inner gill, are de- 
scribed. The structure of Dreissena is intermediate between these, but 
nearer to that of Anodonta. The final conclusion is, that the gill i.s 
