INTRODUCTION 7 



whip-like appendages, or flagella ; with cilia, or motile appendages, 

 similar in general form to eyelashes ; with changeable processes, or 

 psendopodia ; or with no motile apparatus whatsoever ; forms of the 

 most diverse size and shape, including many higher Metazoa, such as 

 worms, rotifers, ctenophores, crinoids, and crustacean larvae, as well 

 as many plants, were all described as " animalcula." Descriptions of 

 internal organs soon began to accompany the descriptions of types. 

 The contractile vacuole, a characteristic pulsating vesicle of the Pro- 

 tozoa, was discovered by Joblot (1754-' 5 5), who also showed that 

 cilia on Infusoria have a definite arrangement in different 

 species, and that many forms are provided with cuticular stripings. 

 All of these forms, sometimes called insects and sometimes 

 fish, were still generally supposed to be microscopic reproductions of 

 higher animals. Dujardin's criticism of Joblot's work might well be 

 applied to that of many others of this early period : " Several of the 

 figures which he gives," says Dujardin, "bear the impression of a 

 too lively imagination for scientific purposes, and are frequently so 

 bizarre and fantastic as to discredit the use of the microscope." * It 

 is easy to understand this criticism when we think of Joblot's picture 

 of the worm Anguillula with a serpent's head, or the flagellated pro- 

 tozoon Eiiglena with a broad mouth, flagellum, and well-developed 

 mammalian eyes. " For his picture of the ciliate Paramaecium aurc- 

 lia" says Dujardin, " he apparently used his own slipper as a model." 



The life history of a protozoon was first made out by Trembley 

 (i744-'47), who saw the microgonidia or young spore-forms of cer- 

 tain Vorticellidae leave the parent-colony and begin the formation of 

 new colonies by longitudinal division. 



The discoveries made by means of the microscope were regarded 

 with complete scepticism by Linnaeus in his earlier scientific works, 

 and the very existence of Leeuwenhoek's animalcula was at first 

 denied by him, but in the later editions of his Systema Natures they 

 were grudgingly admitted under the significant generic name of 

 Chaos \Chaos proteus (Amceba), CJiaos redivivum, etc.]. The organ- 

 ized nature of Volvox globator, a form which had been discovered and 

 fairly well described by Leeuwenhoek, was admitted at this time, and 

 finally, in the twelfth edition (1767), the animal nature of a Vorticella. 



Many of the early investigators studied the Animalcula from the 

 physiological standpoint, and attempted to ascertain the functions of 

 many of the so-called organs. Their efforts were often strikingly 

 successful and have been confirmed by later observations. Corti 

 (1774), Spallanzani (1776), and Gleichen (1778) are the most familiar 

 names in this line of research. Corti and Gleichen compared the 



1 Dujardin ('41), p. 7. 



