312 SCIENTIFIC ILLUSTRATIONS [Sel 



lined with silk, from which threads issue in every direction, 

 and are fastened to the surrounding plants. Mr. Thompson 

 says that in this cocoon, which is open below, she watches for 

 her prey, and even appears to pass the winter, when she closes 

 the opening. It is most commonly, yet not always under water, 

 but its inhabitant has filled it for her respiration, which 

 enables her to live in it. She conveys the air to it in the 

 following manner : she usually swims on her back to the 

 surface, then she turns over and jerks a bubble of air under her 

 abdomen, and appears like a globe of quicksilver. With this 

 she enters her cocoon, and displacing an equal mass of water, 

 ascends again for a second lading, till she has sufficiently filled 

 her house with it, so as to expel all the water. How these 

 little animals can envelop their abdomen with an air-bubble 

 and retain it till they enter their cells, is still one of Nature's 

 mysteries. It is a wonderful provision which enables an 

 animal that breathes the atmospheric air to fill her house with 

 it under water, and by some secret art to clothe her body 

 with air as with a garment, which she can put off when it 

 answers her purpose. This is a kind of attraction and repulsion 

 that mocks all inquiries ; and man's inventions of the diving 

 bell and the air balloon, to enable him to investigate sea and 

 sky, and his many other successful achievements over the diffi- 

 culties of circumstance, are scarcely more astonishing. p. 



S elf-Dependence a Condition of Power. 



M. Gue"rin-Meneville has called the silkworm " the dog of 

 insects," for it has been domesticated from the most ancient 

 times. But in losing its self-dependence it has been deprived 

 of great part of its strength. The moth of the silkworm can 

 no longer keep its position in the air, or on the leaves of the 

 mulberry, when they are agitated by the wind. It can no 

 longer protect itself under the leaves from the burning heat of 

 the sun and from its enemies. The female, always motionless, 

 seems to be ignorant of the fact that she has wings. The male 

 no longer flies ; he flutters round his companion without quit- 

 ting the ground. It ought, however, in the wild state to be 

 possessed of a sufficiently powerful flight. Mr. C. Martins 



