82 



ZOOLOGY 



SECT. 



Systematic Position of the Example. 



Monocystis agilis is a species of the genus Monocystis, belonging 

 to the family Monocystidce, of the order Gregarinida It is placed 

 in the Gregarinida on account of being free and motile in the tro- 

 phozoite state. The absence of partitions dividing the protoplasm 

 into segments indicates its position among the Monocystidse. 

 Monocystis is distinguished by its elongated form, by the absence 

 of any special apparatus in the cyst for the liberation and dispersal 

 of the spores, and by its spindle-shaped spores with thickened 

 ends, each producing 4 8 falciform young. The differences 

 between the species of Monocystis depend largely upon size. 



ORDER 1. GREGARINIDA. 



All the more typical members of the class belong to this 

 group. With the exception of Monocystis, already described, the 

 only genus to which it will be necessary to draw attention is 

 Gregarina (Figs. 62 and 63), the various species of which are 

 parasitic in the intestines of Crayfishes, Cockcoaches, Centipedes, 



dcu, 



spd 



FIG. 6'2. -Gregarina. A, two specimens of G. blattannn partly embedded in enteric 

 epithelial cells of Cockroach ; B 1 , B-, two specimens of G. di(,m-ifiiu ; in B- the epimerite (.;>.) 

 is cast off ; C, cyst of <?. bln/tun'm, from which most of the spores have been discharged; 

 D, four stages in the development of G. {tirtant<:a. c>i. cyst ; den., deutomerite ; c/>. epimerite ; 

 ft. gelatinous investment of cyst; nu. nucleus ; pr. protomerite; -j>xd. 1, short pseudopod; 

 psd. ,?, long pseudopod ; sp. mass of spores ; spd. sporoducts. (From Biitschli's Protozoa.) 



and other articulated animals. It differs from Monocystis in 

 having the medullary protoplasm of the adult divided into two 

 sections, an anterior, the protomerite (pr.), and a posterior, the 

 deutomerite (deu.\ in which the nucleus is situated. Anteriorly 



