56 CORRESPONDENCE. 



This seems to assert that all the Flagellata have one flagellum. 

 A great many of the Flagellata have two, three, or more flagella. 



3. — On page 250 it is stated that when Vorticella divides by 

 longitudinal fission, one of the zooids swims away by means of 

 the cilia, which, when the animal is fixed, make a whirlpool to 

 catch its food. 



I do not believe that there is any authority for this statement. 

 As far as my own experience and reading goes, the zooid which 

 becomes free develops a supplementary ring of cilia towards the 

 base of the body, and it swims away, so to speak, tail-foremost. 

 When it has found a convenient place for settling down, it fixes 

 itself by this temporarily foremost end, and proceeds to grow a 

 stalk ; the supplementary row of cilia is absorbed, and the cilia 

 round the mouth developed. 



4. — On the same page, encysted Vorticellse are said to give 

 birth to sucker-bearing animalcules, which subsequently become 

 Vorticellse. 



This is the celebrated Acineta theory of Stein, which was 

 started by that distinguished naturafist in 1849, and fully 

 developed by him in his work pubUshed in 1854. But Claparede 

 and Lachmann conclusively showed, in their works published 

 between 1855 and i860, that these supposed young are really 

 parasites belonging to a totally different and higher group of the 

 Protozoa. Stein himself has abandoned the theory in his later 

 works, and it will not be found in any recent text-book. Now-a- 

 days no one holds this theory, or has done for the last 20 years. 



5. — On p. 251, in the description of Paraincecium^ it is stated 

 that the function of the contractile vacuoles is to force out the 

 fluid contained in them, and to carry it along tubes all through 

 the body. This process is said to be analogous to the circulation 

 of the higher animals, the vacuole is called a heart, and the 

 radiating tubes blood-vessels. 



The tendency of all recent investigations has been to show that 

 the radiating tubes act simply as drain-pipes, to collect the liquid 

 from the general mass of the protoplasm, and convey it to the 

 contractile vesicle, which, in contracting, expels it from the body. 

 Fine openings have been seen on the exterior leading to the 

 vesicle. In ParamcEciiim^ when the vesicle contracts, the rosette- 

 like tubes remain filled, and this fluid seems to fill the vesicle 

 when it next expands. If this view is correct, and it is the 

 generally accepted one, there is no real resemblance to a heart. 

 Mr. Hoyle says his readers are not likely to see these rosette 

 tubes ; this is true if the animals are freely swimming about in a 

 healthy condition, but confinement and pressure in a live box, 

 or compressorium, produce them pretty easily. 



