120 ANATOMY AND LIFE HISTORY OF MOLLUSCA. 



pinnae supported the lamellse of the usual gill-like pattern. I 

 believe it is not at all uncommon in Botany Bay for similar large 

 specimens to be washed up upon the beach. 



Amongst the Lamellibranchiata the gill plates are associated 

 with the organs of locomotion. Thus in Lima multicostata, Sow., 

 which is not uncommon on the north-east coast about the Barrier 

 Reef, we find the mantle-margins separate and the inner margin 

 fringed with long tentacular filaments. These are of a deep 

 crimson color, with transverse lines upon them which make them 

 look as if they had spiral lines inside. The animal swims with a 

 gentle opening and closing movement of the valves, making it 

 progress in a series of small jerky movements. The filaments of 

 the fringe are thus always in movement backwards and forwards, 

 and the water is thrown in a series of waves on to the gill-plates, 

 giving a stream of water for respiration such as would be supplied 

 were the animal possessed of a siphon. It is a singularly beautiful 

 Molluscan gill, and a similar species has attracted the notice of 

 naturalists in Britain. Unfortunately a little touch with the 

 hand breaks off the filaments. They form most interesting objects 

 under the microscope, and continue moving for several hours after 

 being detached from the animal. 



The gill of our common oyster (Ostrcea mordax, Gould,) forms 

 an important and valuable subject for microscopists, which is 

 always within our reach. The different filaments are seen to be 

 united, as it is termed, by concrescence. Between each of them 

 there is a double layer of chitinous rods, each layer being separated 

 by a series of cells lined with ciliated epithelium. These are the 

 apertures between the filaments. Besides the chitinous rods there 

 are transverse divisions between the gill-chambers, consisting of 

 horizontal fibres between each of the apertures. The surface of 

 the whole gill is thickly covered with ciliated epithelium, larger 

 on the divisions, and these cilia keep up a continual stream of 

 water. In this species they are of unusually large size. 



The gill-plates of some of the families of bivalves are united 

 together. In the Mytilidae or mussels this union is small in 

 amount, and gives rise to two orifices, anterior and posterior, the 

 larger of which is the anterior one, and this serves as an outlet 

 for the foot, while the posterior outlet allows the excreta and the 

 water which has been used for respiration to pass out. If the 

 common mussel, Mytilus hirsutus, Lam., is taken alive and placed 

 in the water, this movement can be watched and the whole process 

 seen distinctly. If also one of the common Arcade, such as 

 Area trapezia, Desh., be taken, it will be found that the gills are 

 united posteriorly to a membranous septum. In the common 

 Trigonia pectinata, Lam., or lamarckii, Gray, the mantle-lobes 

 correspond with the grooves of the shell, so that it appears to be 



