58 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



the othei' would amount to nothing less than a metamorphosis, none 

 of the steps in which have been observed. 



Another point of difficulty is the entire absence in the supposed 

 young of any partition separating the luicleus-bearing anterior portion 

 of the organism from the posterior portion. 



The other forms, resembling those which Leidy thinks may also be 

 young of Triconympha;, I have represented in Figures 30-32, 35-39, and 

 42—44. 1 can see no sufficient reason, however, for supposing them to 

 be young Trichonymphse. The nucleus of these forms is situated at the 

 extreme anterior end of the body. The anterior tip terminates in a 

 rounded projection, but it has not the form of the knob seen in Figures 

 27 and 29, and a comparison with the cap seen in adult Trichonymphse 

 is more difficult in this case than in that of the forms last described. 

 The cilia are of very nearly equal length over the entire body. They 

 are arranged in bands running spirally ai'ound the animal, and the 

 spirals run in the same direction (dexiotropic) as in the forms we have 

 just been discussing. 



There are, however, so many points of difference between these two 

 kinds of supposed young parasites as to render it probable that they 

 are not connected with each other genetically any more than they are 

 with Trichonympha. It will be observed not only that the nuclei are 

 differently situated in the two forms, but also that in those shown in 

 Figures 30-32 and 35-38 the interval between successive bands of cilia 

 remains nearly constant throughout the entire length of the animal, quite 

 unlike the condition obtaining in the other forms. 



This form is also found in a great variety of sizes (Figs. 30, 31, 35), 

 the largest being considerably larger than the individuals of the other 

 form represented in Figures 27 and 28. The shape of tiie animal is char- 

 acteristic, being in the living condition long and slim. Figures 37, 39, 

 and 42-44 represent living specimens. Figure 38 shows one that died in 

 normal salt solution. Figures 30-32, 35, and 3G represent the shapes 

 they assume when killed with coi-rosive sublimate. Their method of 

 locomotion also serves to distinguish them from the forms which I have 

 last described, for they often move, independently of ciliary activity, 

 by changes in the form of the whole body (Figs. 39, 42, 44), — some- 

 times with the wriggling, squirming motion of a worm, at others, swell- 

 ing out in places to almost double their average diameter, and then 

 slowly contracting their body-wall (Fig. 44), they produce a kind of 

 peristaltic motion, which may aid in locomotion. The smaller ones 

 (Fig. 43), when travelling very rapidly in a straight line, revolve around 



