THE YOUNG 



NATURALIST. 



103 



September (continued.) 

 A. betularia P. tetraquetrana 



T. extersaria G. proximella 



C. rotundaria A, torquatella. 



The above comprise those which regularly 

 feed on Birch, the list might be consider- 

 ably extended by including those which 

 sometimes, by force of circumstances, feed 

 upon it, but this was not thought desirable. 



HYMENOPTEARA. 

 Tentheridinid.5: (Saw Flies). 

 Tenthreda olivacea. 



,, viridis (?) Aug. to Oct., Olive. 

 Tenthredopsis scutellaris, com. 

 inornata. 



Eriocampa annulipes, July to Sept. ( Head 

 brown, hodyyellorv or white, shining. 



Blennocampa betuleti, rai'e. 



Phyllotoma nemorata, Juns, July, September 

 and October ; mines leaves. 



Fenusa pumila, June, July, August a-nd Sep- 

 tember ; mines leaves, 



Fenusa betulae, June amd Sept. ; mines leaves 

 The larvae of many of the sawflies are 



yet unknown, and consequently their food 



plant is unknown ; a wide field, therefore, 



exists for discovery here. 



PSYLLIDiE (ImAGOS.) 



Psylla sylvicola (on B. verrucosa ), May. 

 ,, Lowii, November and February. 

 mali, Jime to August. 

 Trioza albiventris, October, 

 Aphalara polygoni, May to October. 



A. SEA-SQUIRT. 



By J. W. Williams 

 {Univ. Dunhelm), Honarary Member 

 Boldmere Naturalists' Society. &c., &c. 



The sea-squirts, or as they are known 

 scientifically, AscidianSs may be found, 

 especially after a storm, attached to sea- 

 weeds and shells thrown upon the sea-shore. 



They take their popular name from the 

 peculiarity they possess of discharging when 

 touched a jet of water, and their scientific 

 one (Gk. askos, a wine bag) because they are 

 generally shaped somewhat like a double- 

 necked bottle. 



The covering of a sea-squirt will be found to 

 consist of two layers — an inner and an outer 

 — the former called the mantle, and the 

 latter the test or external tunic. The test 

 has a rough and leathery texture, and con- 

 tains, strange to say, a substance identical 

 with the cellulose of plants. The mantle, 

 on the other hand, is muscular, and it is by 

 means of its contractibility that the animal 

 is enabled to throw out those peculiar jets 

 of water I have spoken of. 



At the apex of the sea-squirt there are 

 two apertures which lead into the interior 

 of the animal, and through which water is 

 incessantly circulating, coming in at one 

 aperture — the upper one known as the in 

 gestive or branchial aperture — and going 

 out at the lower or atrial aperture. The 

 branchial aperture is generally surrounded 

 with a circlet of small tentacles, and opens 

 into a large chamber known as the branchial 

 sac. The lower extremity of this sac leads 

 by the gullet into a capacious stomach, 

 which is succeeded by an intestine opening 

 into a cavity connected with the atrial 

 aperture known as the cloaca. 



The walls of the branchial sac are richly 

 supplied with blood-vessels, and it is very 

 easy to understand how respiration is 

 effected, viz., by the aeration of the blood 

 contained in those vessels, by the water 

 which is constantly circulating through the 

 branchial sac — the water, of course, con- 

 taining, as it always does, air in solution. 



Qirculation is effected in a manner quite 

 as simple. The heart has, unlike that in 

 most animals, no valves, and consists of a 

 simple muscular tube open at both ends. 

 The blood is propelled by the peristaltic 

 movements of this organ, and, yih^t \^ fx- 



