THE SPOROZOA 



155 



(vesiculae seminales) of the earthworm (Lumbricus spp.). This 

 species is not only very easily obtained, but is also a very typical 

 example of the class ; hence in describing the various phases of its 

 life-history it will be possible at the same time to introduce and 

 define the terminology to which we shall adhere in the sequel 



Fio. 2. 



Trophozpites of Monocystis agilis. a and 6, 

 young individuals showing changes of body- 

 form due to contractility, c, an older in- 

 dividual, still enveloped in a coat of sperma- 

 tozoa, (a and 6 after Stein, c after Lieberkiihn, 

 from Lankester.) 



Flo. 3. 



Trophozoites of Monocyntis 

 magna, attached to the seminal 

 funnel of Lumbricus. a, young 

 individual; 6, goblet shaped 

 epithelial cells of the seminal 

 funnel, in which the extremity 

 of the parasite is inserted. 

 (After Biitschli, from Lankes- 

 ter.) 



for the corresponding 

 stages of other Sporo- 



zoa. It should be understood, however, that the form 

 which can be selected as most typical of a group is not 

 necessarily the most primitive of its members. From the 

 type chosen we shall have to work backwards to simpler 

 forms, as well as forwards to more complex. 



The earthworm is infested by various species or varieties 

 of Monocystis; according to Cu4iiot [13] by no less than seven 

 or eight species, of which four are stated to be of common 

 occurrence, namely, M. magna, A. Schmidt ; M. lumbrici (Henle) 

 ( = M. agilis, Stein) ; M. pilosa, Cuenot ; and M. porrecta, A. 

 Schmidt. The specific distinctness of all these forms cannot 

 be unhesitatingly conceded, but at least two distinct species, 

 probably with several varieties, are generally recognised, and are 

 to be found in almost every worm, viz. M. magna and M. agilis. 

 The two species differ in size and in other specific details of 

 character. M. magna (Fig. 3) is the larger of the two, and 

 occurs attached by one extremity of the elongated body to 

 the epithelium of tbe seminal funnel, only quitting this situa- 

 tion at tbe period of conjugation, when it drops off into the 

 sperm-sac. M. agilis (Fig. 2) is found in the interior of the 

 clumps of developing spermatozoa, or floating freely in the sperm- 

 frequent occurrence in the zoological nomenclature of just the commonest or most 

 familiar forms of life, particularly amongst the Sporozoa. According to Labbe 

 [4] the species under consideration should be called Monocystis tenax (Dujardin) ; 

 according to Cuenot [13] its proper designation is M. lumbrici (Henle). We refer 

 to these authors for a discussion of these knotty questions, and retain here the name 

 most generally employed, in this country at least, for the species. 



