GREGARINHLE 77 



The contents of the seminal vesicle will be found to consist almost 

 entirely of seminal cells and mother-cells in different stages of develop- 

 ment. Among them, Gregarine forms, both encysted and free, will 

 be seen in large numbers, though the free forms may be absent 

 altogether. 



Several different species of Gregarine are parasitic in the seminal 

 vesicles of Lumbricm terrestris, L. (also known as L. herculeus, Sav., 

 and L. agricola, Hoffm.), the largest of our native earthworms. Of these 

 very little is known, but it is certain that they all come under the 

 heading of monocysts. The species most frequently encountered is 

 Monocystis lumbrici (Henle), better known as M. agilis, Stein. On 

 account of its extreme motility it makes a very 

 good subject for examination. Although very 

 small in size, measuring only about 0'2 to 0'3 mm. 

 in length, its comparative opacity renders it 

 easily discernible with a low power lens. 



The living Gregarine shows a marked differen- 

 tiation of the granular endoplasm from the hyaline 

 ectoplasm. At the margin of contact there is a 

 single layer of very fine, closely packed, spincter- F IG . 21. Monocystis 

 muscle fibrillse, while the body surface is covered lumbricis (Henle) in 



.,, . , . ,., . !/ i ^ -i i two different stages of 



with a thin cuticle in which a fine longitudinal movement. Magnified 

 striation is discernible. 260 : 1. (After Stein, from 



-r* -i- i i.i i Braun.) 



Bending and gliding movements are rarely per- 

 formed by the free-living forms. The most conspicuous motile pheno- 

 mena are the contractions, which give rise to lively streamings of the 

 endoplasm, the granulations streaming away from one end of the body, 

 which swells out and becomes club-shaped, while the opposite end 

 becomes proportionally thinned. Then, almost without perceptible 

 pause, the process is reversed and the streamings run in the opposite 

 direction, accompanied by a corresponding change of body shape. By 

 this process, the bladder- shaped inner body which contains the nucleus 

 is tossed from end to end, scarcely remaining stationary at all. 



The first stage of reproduction consists in the association at their 

 anterior ends of two Gregarines, which then proceed to surround 

 themselves with a common cystic membrane. This process is rarely 

 observed directly, but the young cysts, which are round in shape, are 

 always to be found in the month of May. In them the two Gre- 

 garines are seen to lie side by side but quite distinct from one another ; 

 they are contracted into balls and do not touch the cystic envelope. 

 In a later stage, each of the two Gregarines undergoes reproduction 

 independently of the other, this process resulting in the formation 

 from the peripheral layer of a number of little daughter-cells. In 

 the mature cysts numerous spindle-shaped " pseudo-navicellse " are 



