GENUS ASTASIA. 2)7$ 



Fam. II. ASTASIAD^, S. K. 



Animalcules mostly free-swimming, exceedingly plastic and variable in 

 form, bearing a single terminal flagellum ; oral aperture distinct ; endoplasm 

 colourless. 



Genus I. ASTASIA, Ehr. 



Animalcules free-swimming, ovate or elongate, very elastic and change- 

 able in form, metabolic, invested by a distinct cuticula ; flagellum single, 

 projecting from the more attenuate anterior extremity ; oral aperture 

 situated close to the base of the insertion of the flagellum, highly extensile, 

 continued into a long, straight, tubular pharyngeal tract ; endoplasm 

 transparent, enclosing incepted granules, but not assimilating chlorophyll 

 or other coloured matter ; contractile vesicle and endoplast distinct. In- 

 habiting fresh and salt water. 



Considerable difficulty has usually attended the separation of the members of 

 this genus from those of Euglena, a circumstance that must be attributed to the 

 imperfection of the distinctive characters of the two genera as first laid down by 

 Ehrenberg, accompanied by his inclusion under the same generic heading of animal- 

 cules belonging to each of the two types. Adopting, nevertheless, the distinctions 

 first pointed out by Dujardin, and since recognized by Carter and other later writers, 

 it becomes evident that the genera Euglena and Astasia are not only easily distinguish- 

 able, but appertain to two widely distinct family groups. In accordance with their 

 respective diagnoses formulated in this volume, it will be found that while in external 

 contour and in the remarkable elasticity of the endoplasmic element with its invest- 

 ing cuticula the two generic types bear a considerable superficial resemblance, a 

 strongly marked structural diff"erentiation is developed immediately beneath. One 

 of the most important distinctions that thus presents itself pertains to the characters 

 of the ingestive or buccal apparatus. In Astasia this consists of a large, widely 

 dilatable but simple aperture, continued backwards into a clearly defined pharyngeal 

 tract, through which food-particles of a considerable size are readily transported. In 

 Euglena, on the other hand, the oral aperture, while correlated with a peculiar 

 modification of the anterior extremity of the body, is not dilatable or continuous 

 with a distinct pharyngeal tract, and is capable of incepting food- particles of the 

 minutest comparative dimensions only. The distinction subsisting between the 

 consistence of the endoplasm or parenchyma in the two genera is even more easily 

 appreciated. In Astasia this structural element consists of clear and apparently 

 homogeneous sarcode, similar to that encountered among all the more ordinary 

 transparent Flagellata, coloured matter, if present, remaining distinctly isolated, 

 and clearly exhibiting its extraneous derivation ; neither in Astasia is there ever 

 represented that coloured pigmentary corpuscle, the so-called " eye-spot " of the 

 earlier authors, which, although of uncertain value for the purposes of specific dis- 

 crimination, is broadly characteristic of the group to which Euglena appertains. 

 The endoplasm throughout all the representatives of the last-named genus is further 

 conspicuous for its briUiant colouring, this colouring matter not being held tem- 

 porarily in suspension, but being most intimately incorporated or assimilated with 

 the substance of the endoplasm. 



Dujardin has proposed to separate from the genus Astasia certain species in 

 which the body was of a more globular shape, and the terminal flagellum thicker 

 and more rigid at its base, proposing for them originally the title of Pyronema, and 

 afterwards that of Peranema. Out of the two representative forms of this genus 

 described by that authority, however, one, P. protracta, is now recognized to be 

 identical with Ehrenberg's Trachelius {Astasia) trichophora, while his P. globulus 



