142 RESEARCHES IN HELMINTHOLOGY AND PARASITOLOGY. 



In the Gregarines, so common in several species of our earth- 

 worms, the head cell is absent, and therefore is very properly viewed 

 as of a different genus from the more ordinary Grcgarina under the 

 name of Monocystis. The Monocystis agilis is sausage-like in form, 

 and is usually from i-3d to 3-4ths of a millimeter in length. In 

 movement its contractions may commence at one end and proceed 

 towards the opposite end, or it may commence at both ends, proceed- 

 ing towards the middle, or ma}^ commence in the latter position and 

 proceed towards the ends. 



From the researches of Lieberkiihn and others it appears that the 

 Gregarines of earthworms assume a globular form and become en- 

 cysted, and the granular contents are in a greater measure resolved 

 into navicula-shaped germs, which have been named pseudo-navic- 

 ulse or navicelltC or psorosperms. Lieberkiihn was led to consider 

 the amoeboid perivisceral corpuscles of the earthworm as amoeba- 

 like embryos derived fiom the navicellse, but it is very doubtful 

 whether there is any relationship whatever between the two. Both 

 Gregarines and navicella cysts are met with in the intestine of our 

 common earthworm, but the cysts are to be found most frequenth' 

 and abundantly in the sperm vesicles. In the six vesicles of an 

 earthworm Prof. Leidy had counted 1,540 mature navicella cysts, 

 together with a number of groups of immature cysts. The mature 

 cysts, readily visible to the naked ej^e as minute pearly-white glob- 

 ules, by transmitted light have a peculiar pale-blue hue. They 

 measure about i-^th of a millimeter in diameter. A cyst burst open 

 spread its navicellae over a millimeter square, and was estimated to 

 contain about 2,500. These were quite uniform in size and meas- 

 ured 0.0133 mm. long and 0.00665 broad. 



E. Van Beneden has clearly traced the development of the Greg- 

 arina of the lobster from Amoeba-like embryos, so that it is not 

 improbable that similar embryos may be derived from the navicelke. 



The Gregarines are usually viewed as constituting the lowest class 

 of the Protozoa, and hence the lowest of animals. From their 

 structure and mode of development, Prof. L. considered them as 

 holding a higher rank than Rhizopods, and occupying a position 

 intermediate to these and the Infusoria. 



Prof. L. further stated that in a large earthworm, I.unibriats ter- 

 restris, from the yard of his residence, the posterior pair of sperm 

 vesicles alone contained upwards of a thousand navicella-cysts, besides 

 .several thousand Gregarines, Monocystis aoilis, exhibiting the varie- 

 ties of condition, such as have been represented by Schmidt, Lieber- 

 kiihn, and others. Many of the Gregarines were invested with 



