216 THE MINUTE ANATOMISTS 



He points out that what seem to be two wheels are 

 really the lobes of a single disk, and that the ciliary 

 play is continuous, the direction being counter-clock- 

 wise. He discovered that the tube of Melicerta is com- 

 posed of pellets moulded by the ciliary disk, and laid 

 one by one on the edge of the growing tube. 



Hydra ^ 



Leeuwenhoek was the first to discover and describe 

 (very briefly) this deeply interesting animal. He tells 

 us that it possesses from six to eight horns (tentacles), 

 which can be extended so far that under the microscope 

 they seemed to be several fathoms long ! He found 

 two small polyps attached to a parent, and saw them 

 become free, thus anticipating the most important fact 

 in Trembley's discovery, though forty years were to pass 

 before its significance could be perceived. A parasite 

 (Trichodina) was seen running about on the polyp. 

 The figure of Hydra, though recognisable, is not good. 



Unicellular Animals [Protozoa) 



Hooke's Eotalia and Leeuwenhoek's Nonionina (the 

 latter found in the stomach of a shrimp) were the first 

 recent Foraminifers to be noticed. The observations of 

 living Rhizopods begins with Eoesel, who in 1755 

 described and figured an Amoeba. Except for a slight 

 notice of Euglaena by Harris (1696), the study of the 

 flagellate Infusorians begins with Leeuwenhoek's account 



'■Phil. Tram., No. 283 (1702). Better figures are given shortly afterwards 

 by "a gentleman in the country" (Phil. Trans., No. 288, 1703). The chief 

 faults are that the body of the Hydra is shown as segmented, and that there 

 is an outlet at the attached end. The same paper contains the earliest figure 

 of a diatom (Tabellaria) which I have met with ; the writer at first took 

 the cells for "salts" (crystals), but afterwards thought that they might be 

 plants. 



