188 Transmutation of Form in certain Protozoa. 



Fig. 26 is another similar change, which I have often seen 

 from decided Calhdina or Philodina. 



Fig. 27 shows the profile view, which as it turns again in the 

 drop of water reveals the perfect animalcule in its most active form. 



It would seem here as if there were much reiteration, but in a 

 position such as mine I feel as if every step requires the utmost 

 detail in its construction, lest I should suddenly find myself over 

 head and ears in a quicksand, with only a mare's nest to reward 

 the venture ; but if, as it seems to me, there is firm and solid truth 

 near at hand, the journey to it is worth the attempt. 



It is now my duty to undertake a part of the question which 

 is more than usually difiicult, viz. to show that the great system of 

 classification is on an uncertain basis, and I will take the family of 

 Philodinfea as an example, and I think the Figs. 24 and 25 may 

 assist in showing my point. 



The family is divided by Grifiith and Henfrey, in the ' Micro- 

 graphical Dictionary,' into Callidina, Hydrias, Typhlina, Eoiifer, 

 Actimirus, Monolahis, and Philodina. The characters of some are 

 sufiSciently doubtful to admit of removal at once. Thus Grifiith 

 and Henfrey say, p. 358, of Hydrias cornigera, pi. 34, fig. 39, 

 " probably a young and imperfectly examined Philodina," and of 

 Typhlina, "an imperfectly examined genus of Eotatoria, of the 

 family of Philodinsea ;" and p. 463, of Monolabis, " Eyes two, 

 frontal ; tail-hke foot with two toes ; horns absent." 



Dismissing the former two, Hydrias and Typhlina, as " im- 

 perfectly exaraiaed," we come to Monolabis. Now it is evident to 

 all observers of these Infusoria, that the perfectly formed animal- 

 cules, such as Fig. 24, are very frequently observed to present these 

 marks, tail-like toes two, horns absent, simply because the creature 

 does not remain long enough under inspection. 



I have frequently seen Fig. 24 in such a condition, and the next 

 minute protrude another joint of the tail and expose the two lateral 

 horns above the foot as well as those in the cervical region. I am 

 therefore of opinion that these characters in animalcules of such 

 changeable form are not suflicient to warrant a separation into a 

 fresh class. Let us therefore temporarily dismiss this division, and 

 look at the remaining four. 



Callidina, then, is distinct from Philodina, by the rotatory 

 organ not being furnished with a stalk ; but in the two Figs. 24 

 and 25 (which I have repeatedly seen transmutable) we have no 

 characters by which to divide them. Here we have eyes absent 

 often, because we have not that part sujfficiently developed, as in 

 Figs. 25, 22, 23, or in Figs. 19 and 20. But I cannot persuade 

 myseK that these points, either absent or present, visible or in- 

 visible, at any one observation, are any other indication than the stage 

 at which the animalcule has arrived at the moment of mspection. 



