ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 571 



conclusion of Knut-Dahl, that some of the progeny of the common 

 trout descend to the sea and become sea-trout. In fact, sea-trout form 

 a detached tribe of common trout, recently and imperfectly separated off. 



Occurrence of Gobius orca in Clyde Sea Area.* ■ — Alexander 

 Patience has obtained this species, which is one of the smallest and 

 rarest of European fishes, on three occasions in the Forth of Clyde. 

 The closely allied G. jeffreyssii, which Giinther recorded from three 

 localities in the Clyde, is not uncommon. 



Notes on Polyodon spathula.f — Charles E. Stockard makes some 

 notes on the habits of this fish, which is abundant in some lakes border- 

 ing the lower Mississippi river. He was not successful in getting any 

 embryos. 



The fish may attain a length of about six feet, and often weighs 

 over a hundred pounds. It frequents the deeper parts, and feeds 

 chiefly on small Crustacea, chiefly Copepods. The snout is not essential, 

 and its use is probably rather as a tactile organ than as foraging instru- 

 ment. 



Sensory Reactions of Amphioxus4 — G. H. Parker has studied the 

 West Indian Amphioxus, BrancMostoma caribimum Sundevall, a close 

 relative of the common European form, B. lanceolatum Pallas. It is 

 only very slightly sensitive to light ; it responds to a rapid increase, but 

 not to a rapid decrease. The only known photoreceptors are the eye- 

 cups in the wall of the nerve-tube. It is photokinetic and negatively 

 phototropic. 



Amphioxus is stimulated by water warmer than that in which it 

 lives (31 C°.), and is killed in water at 40° C. or higher. It is also 

 stimulated by water colder than 31° C, and is killed by lengthy exposure 

 to water of 4° C. or lower. It is thermokinetic and negatively thermo- 

 tropic. 



The outer surface, especially the oral hood and the tentacular cirri, 

 is sensitive to mechanical stimuli. Amphioxus is also sensitive to 

 sound vibrations. It is thigmotropic, and slightly rheotropic and 

 geotropic. 



The outer surface of Amphioxus is sensitive to solutions of nitric 

 acid, potassic hydrate, picric acid, alcohol, and to strong ether, chloro- 

 form, turpentine, oil of bergamot, and oil of rosemary, but not to 

 solutions of sugar. It is also stimulated by diluted sea water and by 

 fresh water. Amphioxus is negatively chemotropic. 



The photoreceptors in Amphioxus are anatomically distinct from the 

 receptors for thermal, mechanical, and chemical stimuli, and these three 

 are at least physiologically distinct from one another. 



To all stimuli that induce locomotion, Amphioxus responds by forward 

 movements when the stimuli are applied to the tail, and by backward 

 movements when they are applied to the middle or to the anterior end. 

 The animal generally buries itself tail foremost, and in all probability 

 usually swims tail foremost, though it may reverse both processes. 



* Trans. Nat. Hist. Soc. Glasgow, viii. (1908) pp. 74-6. 



t Amer. Nat., xli. (1907) pp. 752-66 (3 figs.). 



t Proc. Amer. Acad. Arts and Sci., xliii. (1908) pp. 415-55. 



