GENUS ACANTHOCYSTIS— ACANTHOCYSTIS CH^TOPHOEA. 267 



which it lives. The movement is, however, clearly active, as proved by 

 the fact that equally light objects in the vicinity remain quiescent. 



Acanthocystis chcetophora feeds on the smaller algae and animalcules, 

 which are captured in the same manner as with Actinophrys sol. In the 

 gradual approach of food, through the dense forest of rays investing the 

 body, the armor formed by the basal disks of the spines rises in a conical 

 eminence, and opens outwardly so as to allow of the entrance of the food. 

 In the process, a portion of projected protoplasm receives the latter, and 

 the whole together is withdrawn, when the body resumes its regular 

 spheroidal form 



In the act of discharging excrement, a similar process occurs, the armor 

 at some point opening outwardly, so as to give passage to the expelled 

 matter. 



In the movements of the animal, at times slight changes in shape 

 become obvious, from a spheroidal to a more ovoidal and polyhedral out- 

 line. The rays and spines, though ordinarily regularly divergent, may 

 occasionally be seen, at some part of the body, to become more or less 

 convergent, or to a greater degree divergent. 



I think there can be little doubt that Acanthocystis chcetophora is the 

 same animal as the one described by Ehrenberg under the name of Actino- 

 phrys viridis This, however, appears to have been previously described 

 by Schrank, with the name of Trichoda chcetophora, and the original de- 

 scription applies so well to the creature in question, that, according to the 

 rules of zoological nomenclature, I have adopted for it the earlier specific 

 name.* Ehrenberg himself remarks, in reference to his description of 

 Actinophrys viridis, that he had overlooked Schrank's form, which may 

 probably be the same, and in which case his specific name should be 

 preferred.! 



I have commonly observed Acanthocystis chatophora of a bright-green 

 color, dependent on variable proportions of chlorophyl corpuscles, as seen 

 in fig. 1. Rarely, I have met with the same form in all respects alike, 

 excepting in being devoid of the bright-green color, as represented in fig. 4. 

 This colorless form has been described by Professor Greeff under the name 



•The original description is as follows: "Kugelforraig, griin, naeh alien Richtnngen gestralt. 

 Allenthalben ziemlich dicht mit crystallhellen Haaren besetzt. Bewegung langsam fortschreitend, 

 oline alle Bewegung der Haare." 



t Infusionsthierchen, 304. 



