52 



PROTOZOA. 



are retractile, and tlie prehensile do not seem to differ materially in 

 function from the suctorial.* In their retraction they often become 

 marked by a peculiar spiral wrinkling of their surfaces possibly due 

 to torsion. 



Mouth (other than the tentacular pores) and anus are not present. 

 Contractile vacuoles are present and vary in number. The macro- 

 nucleus may be elongated or branched, attaining a great extension 

 and complexity in such a form as Demlrosorna, which looks like a 

 colony of Acinetans attached to a creeping stolon. A micronucleus 

 is certainly present in some forms, and probably in all. The body 

 1ms a pellicle which is in some cases thickened to form a shell or 

 theca. The stalk of attachment, when present, is not contractile. 



N 



FIG. H.Epliclota (fodophrya) geMniijiru-n, after R. Hertwig. a, with extended tentacles 

 (both prehensile and suctorial) and two contractile vacuoles; /', the same, with ripe buds 

 into which processes of the branched nucleus N enter ; c, free young form. 



Reproduction takes place in one of three ways : 



1. Equal transverse fission; as a result of thife the organism 

 divides into two equal pieces, one of which the distal retracts 

 its tentacles, acquires cilia, and swims away, while the other, or basal 

 piece, keeps the old attachment and condition. Such reproduction, 

 in which the products are more or less equal in size, is found in 

 Hypocoma, Splicer opliry a, Poiloplirya, Urnula, etc. 



2. Simple to multiple budding ; this is characteristic of the genus 

 Eplielota (Fig. 44). One or more buds, each containing a process of 



'' The prehensile tentacles when present first seize the prey, bring it within 

 reach of the knobbed tentacles ; but it is by no means clear that they do not 

 share in the suction act. 



