i893. NOTES AND COMMENTS. 9 



bivalved mollusca ; and he publishes the following scheme in the 

 Zoologischev Anzeiger for October 24 (vol xv., pp. 373 — 375) as most in 

 accordance with the existing state of knowledge : — 

 Class : Lamellibranchiata (Pelecypoda). 



Sub-Class I: Protobranchiata. — With double comb-shaped 

 gills ; hinge toothless or with interlocking denticulations of 

 the hinge-border or taxodont. Families : Vlastidae, Cardio- 

 lidae, Antipleuridae, Lunulicardiidae, Praecardiidae, Silurinidae, 

 Protomyidae [Solcnoviya] , Solenopsidae, Grammysiidse, Posi- 

 donomyidae, Daonellidae, Nuculidae. 



Sub-Class II. : Desmodonta. — With double lamellar gills ; hinge- 

 teeth wanting or irregular, arising in intimate connection 

 with the ligament supports. Families : Pholadomyidae, 

 Myidae, Anatinidae, Panopaeidae, Septibranchia, Mactridae, 

 Pholadidae, Gastrochaenidae. 



Sub-Class III. — Ambonodonta. With double lamellar gills ; 

 hinge-teeth inclined backwards on the hinge-plate of the 

 shell, variable in position, may be wanting. 



Order i. Eutaxodonta. With taxodont hinge. Family: 

 Arcidae. 



Order 2. Heteyodonta. With heterodont hinge. Families : 

 Astartidae, Crassatellidae, Chamidae, Lucinidae, Cardiidae, 

 Tridacnidae, Cyrenidae, Cyprinidae, Veneridae, Solenidas, 

 Tellinidae, Donacidae. 



Order 3. Schizodonta. With schizodont hinge. Families : Tri- 

 goniidae, Najadae. 



Order 4. Anisomyavia. Hinge-teeth wanting, or if present, isodont 

 or irregular ; with two very dissimilar hinge-muscles or 

 merely a single hinge-muscle. Families : Aviculidae, Myti- 

 lidae, Pinnidae, Pectinidae, Spondylidae, Ostreidae, Anomiidae. 



The Curvature of Plants. 



Mr. Francis Darwin and Miss D. Pertz have lately been 

 studying the artificial production of rhythm in plants, and the 

 results appear in the last number of the Annals of Botany. The obser- 

 vations were made with the help of a new machine devised by the 

 authors, which they call an intermittent klinostat. It differs from the 

 ordinary klinostat in that movement is allowed only at regular 

 intervals. The spindle is connected with a clock in such a way that 

 a half rotation, i.e., of 180 degrees, occurs at the end of every half- 

 hour. Experiments were made with relation both to geotropic and 

 heliotropic curvatures. In the former series, shoots of valerian and 

 stalks of dandelion were used ; these were fixed through a bored cork 

 in test-tubes of water, which were attached horizontally to the 

 spindle. The machine was placed opposite a window to cancel the 

 effect of light in causing curvatures. When the clock was working, 

 the influence of gravity on the growing shoot or stalk was, of course, 

 reversed every half-hour, and it therefore received a stimulus of equal 

 duration to curve towards opposite sides. 



After the first few half-hourly intervals, the curvatures in either 

 direction continued regularly for about thirty minutes. If the clock 



