SCIENTIFIC RECREATIONS. 



resemble the microscopic fungi, whose germs are diffused in the same way. 

 When once they have obtained the means of development, they multiply 

 with incredible celerity. If the decaying vegetable or animal substances be 

 carefully excluded from contact with the air, or if the air be heated before 

 it is admitted to them, no infusoria will appear. They are rarely developed 

 on mountains of a certain height, where the atmosphere is free from foreign 



bodies. 



Though these animalcules are so exceedingly minute, yet the forms 

 exhibited by them are extremely various, and some of 

 them present also considerable variety in the forms 

 assumed by the same individual under different cir- 

 cumstances. In many species the soft body is enclosed 

 in a firm integument, strengthened by a deposit of sili- 

 ceous matter ; these envelopes, which are often preserved 

 after the death of the animals, are termed the shields, 

 and the animalcules encased in them are called loricated 

 Fig. 8 3 i.-voivox gbbator. infusoria> The rem arkable discovery has been made that 

 large distinct beds of former formations are entirely made up of the accumu- 

 lated remains of these animalcules. 



We arrive at the HYDROZOA after leaving the Infusoria, and find 

 ourselves in the sea, and far from land, where it will be difficult for us 

 to ascertain the characteristics of these interesting animals. But for- 

 tunately we can obtain much nearer home, and occasionally in a private 

 aquarium, a specimen of the hydrozoa which will serve our purpose, 

 as it has served before to introduce readers to the study of these water- 

 ! polypes, some of which are so like plants that they are frequently mistaken 

 for them. 



The hydrozoa present a " definite histological structure," says Professor 

 : Huxley ; " the body always exhibits a separation into 

 at least two distinct layers of tissue, an outer and an 

 inner." The Hydras, or fresh-water polypes, which may 

 be found in nearly every pond adhering to the duck- 

 weed, appears like tubes, and if touched will curl up 

 into tiny knobs. But if let alone they will adhere to a 

 glass by their single foot, or sucker, which can be 

 moved at pleasure. 



The foot, or sucker, is continued to a slender 

 cylindrical stalk, from the end- of which radiate a 

 number of tentacles, or " feelers,", growing around the 

 mouth, and serving to convey or attract food to the 

 animal which is, so to speak, all stomach. There is 

 no breathing apparatus, and what food it cannot digest 

 is expelled from the mouth. The peculiarity which 



has given the hydra its name is, that no matter into how many, pieces you 

 cut this polype, the parts cut off will all develop into little polypes perfect 



