THE OPALINID CILIATE INFUSORIANS. 65 



other species, has two sorts of indiAiduals ; those of an elongated 

 form, figure 37, a to f, and others which are ovoid, figure 37, d and e. 

 Besides these there are many intermediate individuals. Some of the 

 large individuals seem to arise from ordinary elongated forms by 

 increase in thickness. Leger and Duboscq write : 



The elongated forms result from longitudinal division, while the massive 

 forms are produced by transverse fission. 



Study of conditions in P. caudata, Cepedea dimidiata, and other 

 species with both slender and stocky forms, causes me to doubt if the 

 matter is quite so simple as this, and the doubt is emphasized by study 

 of Leger and Duboscq's figures. In their figures of the ovoid forms 

 the ectosarc is enormously thickened and contains large inclusions of 

 the pseudo-oily nature, while in the elongated forms the ectosarc is 

 much thinner and its inclusions smaller. I am more inclined to sus- 

 pect that the ovoid form may be associated with peculiar nuclear 

 phj'siological phenomena rather than with the manner of division. 

 I have found some of the stocky forms of P. caudata with greatly 

 enlarged nuclei. I am, however, unable to suggest the nature of the 

 nuclear condition which may be associated with the thickening of 

 the bod3\ 



The cilia are longest anteriorly, diminishing in length posteriorly, 

 the posterior portion of the body being naked. Leger and Duboscq 

 say that there are about 20 longitudinal spiral lines of cilia upon an 

 ordinary elongated individual of average size, and that the distance 

 between them is constant — about 0.003 mm. This statement that the 

 intervals between the lines of insertion of the cilia are uniform 

 is of interest. In nearly all species of all four genera of Opalinids 

 which I have studied the cilia line interspaces in the anterior end of 

 the body are but one-half, or one-third, or even in one species but 

 one-fourth as great as they are posteriorly. According to Leger 

 and Duboscq, in P. saturnalis the cilia lines are no more closely set 

 anteriorly than they are poster iorlj'. 



Leger and Duboscq describe a single minute individual (fig. 37, h) , 

 which, from its form and its long sparse cilia, is either a microgamete 

 or a microgamete mother cell (see Metcalf, 1909). It needs but a 

 ball of sticky protoplasm near its posterior tip to be a typical micro- 

 gamete, even to the right angle bend at the base of the "tail." This 

 individual is of great interest. It indicates that fertilization prob- 

 ably takes place in the intestine of the same individual hosts which 

 bear the full-sized Opalinids. It is of interest, too, to note that 

 encysted forms and individuals hatching from the cyst (fig. 37. r/) 

 are also found in these same adult hosts. It looks as if all the life 

 history of the parasite occurred within the intestine of the adult 

 Box hoops, so that there is not. in the case of this host, a restriction 



