io8 PROTOZOA. 



emerges and becomes a cellular parasite. The spore of G. 

 giganiea, the species inhabiting the lobster's intestine, is non- 

 nucleated and somewhat globular. It forms two processes, 

 of which one remains short and motionless, while the other 

 growing long and vibratile, becomes nucleated, and is 

 detached. The other part seems to come to nothing. 



Monocystis — a type of those Gregarinida or Sporozoa in 

 which the cell is not divided into two parts by a partition. 



Two species of Monocystis {M. agilis and M. magna) 

 infest the male reproductive organs of the earthworm so 

 constantly, that we are almost always sure of finding them. 

 The full-grown adults are visible to the naked eye. They 

 are somewhat cylindrical cells, but change their form as they 

 sluggishly move. There is a definite contractile cortex, and 

 a large nucleus in the central substance. 



Let us begin with a young form parasitic within one of the 

 reproductive cells of the earthworm. It grows and becomes 

 free from the cell. In some species, the curious end-to-end 

 adhesion of two individuals has been observed. Encystation 

 occurs, involving a single individual or two together. Within 

 the cyst, orderly nuclear division results in the formation of 

 spore-forming masses. These form elliptical spore-cases or 

 " pseudonavicellEe," enclosed in a firm sheath. Each 

 spore-case contains several, usually eight spores, lying around 

 a residual core. The cyst bursts, the spore-cases are extruded, 

 the spores emerge from the firm cases. The young spore 

 is more active than the adult, indeed, in some Gregarines it 

 is for a brief period flagellate, then amoeboid, then like the 

 sluggish adult. Intra-cellular parasitism and copious food 

 naturally act as checks to activity. 



SYSTEMATIC SURVEY OF PROTOZOA. 

 Most Protozoa are unicellular animals. 



A. — Primitive Forms. 



I. Proteomyxa. — A class established by Ray Lankester, and de- 

 scribed by him as " a lumber-room in which oljscure, lowly-developed, 

 and insufficiently known forms may be kept until they can be otherwise 



