PROTOZOA. 639 



and hence " worms and the larvse of insects die suddenly from 

 the touch of these gelatinous threads." 



The Hydridae increase by minute gemmules or buds developed 

 from the common substance of the body ; but unlike some of the 

 Zoophytes, the point of union becomes more and more tender, 

 and they are finally detached. These polyps may be artificially 

 increased. If the body be divided, each segment will become a 

 new animal, and even " a small portion of the skin soon grows 

 into a polyp. If cut off pieces be placed in contact, and pushed 

 together with a gentle force, they will unite and form a single 

 one." One species, it is said, "can be actually turned inside out 

 like a glove, and yet perform all the functions of life as before, 

 though that which was the coat of the stomach is now the skin 

 of the body, and vice versa." (Gosse.) This power of repro- 

 duction gave to this polyp the name of Hydra, in allusion to the 

 fabled monster whose heads sprouted as often as they were cut 

 off by Hercules. 



FOURTH CLASS. PROTOZOA, (Gr. Ttgaws, protos, first, or lowest; 

 wo*>, zdon, animal.) INFUSORIA. FORAMINIFERA. RHIZO- 

 PODS. 



The above several names are applied to minute animals which 

 have been observed and studied since the discovery and improve- 

 ment of the microscope. Leeuwenhoek, in 1675, first observed 

 them in standing water, though he was not then certain as to their 

 animal nature. They are termed PROTOZOA, because regarded 

 as the first manifestations of animal life. Being found in infu- 

 sions of vegetable and animal substances, they are called INFU- 

 SORIES, though infusion is not essential to their production. Some 

 of them are minute shells, consisting of one or more chambers, 

 united by a small perforation or foramen, and are hence named 

 FORAMINIFERA. The term RHIZOPODS, (Gr. rhiza, a root ; pous, 

 a foot,) is also applied to these latter animals. 



The Infusories have been divided into the " illoricated " and 

 the " loricated," the former composed of a single, homogeneous, 

 soft substance, analogous to fine membrane and unshielded or 

 naked ; the later covered by a siliceous or calcareous lorica, or 

 external shield, in which the animal is enclosed. The pellucid 

 membrane of the animal contains, according to Ehrenberg, a 

 long curved intestine, with numerous globular bodies suspended 

 to it somewhat like grapes. These he regarded as so many 

 stomachs, and therefore called the animals POLYGASTRICA, (many- 

 stomached,) dividing them into two legions : 1. ENTERODELA, 



