138 



GENERAL BIOLOGY 



entry of oil into the breathing tubes, thus asphyxiating the wrigglers. 

 It has been thought that certain kinds of fish destroy eggs and wrig- 

 glers. Muttkowski personally examined over 6,000 of these fish-stom- 

 achs and found only one mosquito wriggler. Another observer exam- 

 ined about 2,000 specimens of Gambusa, the so-called "mosquito-de- 

 stroying top minnow," and found mosquito w r rigglers in only about 2% 

 of the fish. 



PARAMOECIUM 



The. animal now to be studied is the Paramoecium (Fig. 52), a 

 member of the class Infusoria.* Paramoecia are often called slipper 



animalculae because they are shaped like a 

 slipper, or more correctly like a cigar. The 

 distinctive characteristic of this animal is that 

 its entire body is covered with little hair-like 

 projections called cilia. The rapid movement 

 back and forth of these cilia (especially those 

 of the oral groove which beat faster than those 

 on other parts of the body), causes the animal 

 to be propelled through the water in which it 

 swims. There is an oral groove extending 

 obliquely backward from the forward end 

 which empties just a little behind the middle 

 portion of the body. The mouth is situated at 

 the end of the oral groove, so that as the ani- 

 mal is swimming along and constantly revolv- 

 ing, various substances are forced down the 

 oral groove and as they reach the end of this 

 groove are thrust into the mouth proper. There 

 is also an endosarc and ectosarc just as there 

 is in Amoeba, but there is also an additional 

 membrane or pellicle, sometimes called the 

 cuticle. This is demonstrated by placing a 

 drop or two of 35% alcohol in a drop of water 

 where some of the Paramoecia are found. The 

 pellicle will then be raised like a blister, show- 

 ing that this part is separate and distinct from the rest of the animal. 

 Immediately beneath the cuticle there is found a layer of spindle-shaped 

 cavities in the ectoplasm filled with a semi-fluid substance. These are 

 known as trichocysts ( ), supposed to be weapons 



of offense and defense (Fig. 53). If a little acetic acid or even ordinary 

 blue or green fountain pen ink is added to the water these trichocysts are 

 exploded, and the long threads which they contain are discharged. 



Fig. 52. 



Paramoecium caudatum. 



1. Mouth at bottom of 

 groove. 2. Oesophagus. 3. 

 Food vacuole just being 

 formed. 4. Contractile vacu- 

 oles. 5. Trichocysts which 

 have exploded ; the unex- 

 ploded ones line the cuticle. 

 6. Cilia. 7. Meganucleus. 8. 

 Micronucleus. 9. Contractile 

 fibrils. (After Butschli.) 



"The early workers in biology took vegetable matter, such as dried grass, and steeped it in 

 boiling water, then letting this infusion stand in the air. The animals found therein were called 

 Infusoria. 



