Ui/(lali)iaea.'\ infusorial ANiMALCULEst 629 



fibres, {ire as distinct as in the larger animals. During the contrac- 

 tion of the body, they become shorter and broader, by -which they 

 are easily distinguished from the other band-like and filiform 

 organs, which only become curved during contraction of the body 

 (maintaining themselves passive). The alimentary canal has no 

 true stomach ; it diminishes posteriorly, and the internal surface is 

 provided with delicate vibratile cilia ; it sometimes appears grape- 

 like, which form little lateral pockets or stomachs : the ova often 

 occupy a large portion of the body. In most cases, the creature 

 fixes itself to a spot by its foot, and lays several eggs upon the same 

 place, one after another, by a sudden contraction ; sometimes, when 

 it is going to lay more eggs, it returns to the original spot. In 

 eleven hours after the eggs were laid, vibration of the anterior cilia 

 was observed, by Ehrenberg, within them ; and in twenty-four 

 hours the young escaped from the shell. Many of the ova have a 

 double shell, and leave a bright space between the two at one of the 

 extremities ; similar ova are found in other Rotatoria, having diff'erent 

 shapes. In these double shelled ova the young are slowly developed. 

 Ehrenberg names them "lasting eggs, or winter eggs." Some 

 eggs are covered with Hygrocrocis, and appear quite hairy ; these 

 have been regarded as the normal state of other ciliated animalcules. 

 Two kinds of disease destroy the Hydatina, and most of the Rota- 

 toria : 1st, the formation of vesicles, or little bladders, which give 

 rise to the appearance of small rings all over the creature ; 2nd, the 

 formation of granules, from which all the internal organs appear as 

 if composed of delicate granules and shagreened ; 3rd, the overgrowth 

 of Algse upon their bodies. Foul water likewise kills them. Fig. 

 394 represents a vibratile animalcule completely unfolded, seen 

 from the ventral surface. The arrows in the alimentaiy canal 

 indicate a decussating, or circulating movement of its contents, 

 produced by delicate internal cilia, and must not be mistaken for 

 the motion of Monads. 



Hydatina brachydactyla. — Body cylindrical, truncated anteriorly, 

 and suddenly attenuated at the base of the foot ; claws short. 

 Found on Hottonia, &c. Length l-144th. Dujardin would include 

 in this genus Hydatina several Rotatoria distributed by Ehrenberg 

 among other genera. He says : " Notwithstanding the presence 



