Prof. Ehrenherg-s Reseat ches on the Infusoria. 21T 

 rent state of tension, which they would undoubtedly do on 

 the contractions of the animal, if their nature was of another 

 description ; and when the two extremities of the body are 

 equally approximated to each other, none of the bands become 

 invisible, but all increase to nearly twice their former breadth, 

 with a corresponding diminution of their transparency. I have 

 entered into these details regarding the appearance of the mus- 

 cular fibres, for the sake of those who may not have had an op- 

 portunity of having seen the animal, for it is sufficient to see 

 them to be at once convinced of their true functions. 



The envelope of the body of the hydatina consists of a double 

 transparent membrane, the two layers of which are in contact 

 with, and scarcely distinguishable from, each other, when the 

 animal is in a state of repose. But, upon the contractions of 

 two or more of the muscles, the internal membrane into which 

 they are inserted becomes separated to a greater or less distance 

 from the external. During the whole of these phenomena the 

 stomach, ovaries, and the whole of the viscera, are perfectly 

 visible through the transparent muscles. 



These principal muscles are four pairs, which take their ori- 

 gin from the opposite ends of the animal, and proceed in a ra- 

 diated manner to be inserted by broad striated bands near the 

 middle of the body (between the fourth and fifth pair of twigs 

 given off from what Dr Ehrenberg calls the great dorsal vessel). 

 The four upper or anterior muscles rise by narrow insertions 

 from the junction of the head with the body at the root of the 

 rotatory organs ; the four posterior or inferior, from the point of 

 insertion of the bifid tail into the body. The extent of inser- 

 tion of these muscles is much greater in the Eospkora, Philo- 

 dina and Rotfer, than in the Hydatina ; in them it reaches at 

 least from the second to the sixth of the above mentioned transr 

 verse twigs *. 



• The following are the names which Dr Ehrenberg gives to these muscles t 



1. Musculus dorsalis anterior, 



2 posterior. 



3. Musculus lateralis dexter anterior, 



4 posterior. 



5. Musculus lateralis sinister anterior, 



6 posterior, 



7. Musculus venlralis anterior, 

 8 posterior 



JULY— SEPTKMBKR ]831. V 



