76 POND LIFE 



1696. The finder described the creature as "an animal like 

 a large maggot, on the tail of which appeared forceps like 

 that of an earwig." 



Some years later, in 1703, Leewenhoch noticed a rotifer, 

 which he depicted as "an animal with two wheels thickset 

 with teeth resembling the wheels of a watch." 



Strangely enough, these two old-fashioned descriptions, 

 when taken together, are accurate enough to help the beginner 

 in recognising rotifers from other micro-organisms. 



All the members of the Rotifera are minute, the giants 

 amongst them being |th of an inch in length, whilst the 

 majority are ^^th of an inch or even less. Before describing 

 the species or their habits, a cursory examination must be 

 made of the little creatures themselves. 



We may roughly divide the rotifer into head, body, and 

 foot. The head consists of the " disc," which bears little hairs 

 known as cilia. These cilia wash the food into the mouth, 

 and from there it passes into the oesophagus (throat). The 

 oesophagus, which is similarly lined with cilia, leads into the 

 gizzard. The gizzard, or mas tax, is an organ especially 

 adapted for crushing. The food then passes into the stomach, 

 an organ also lined with cilia, where digestion takes place. 

 The head contains the brain. Two or more eyes are often 

 present, usually red, and sometimes violet in colour. Certain 

 species, however, are eyeless. The body, which is of such 

 transparency that it allows perfect inspection of the internal 

 organs, is variously shaped. In Synchaeta it is peg-shaped, 

 whilst in Hydatina senta it is wedge-shaped, oval in the 

 Asplanchnaceae, and so forth. In certain species the body is 

 enclosed in a case known as the lorica. Others, again, build 

 cases of pellets, or are surrounded by a tube of gelatinous 

 material. 



The foot in some species is absent, but in the majority it 

 is well developed. It may be retractile or telescopic, and is 

 usually furnished with two or three toes and a special gland, 

 known as the cement gland, which secretes a sticky material, 

 in order to " anchor" the creature, when it so requires. 



In the Bdelloida (leech-like) the foot is telescopic, and re- 

 tracts into the body : like a true foot, it is used for the 

 purpose of walking. When so doing one toe is expanded 

 telescopically and the cement gland comes into action ; the 

 rotifer then " closes the telescope " but does not liberate the 

 foot to do so. Hence the body is drawn towards the toes. 

 The foot is then released, and is again stretched to its full 

 length. Sometimes the movement is contrariwise, that is to 



