THE INTESTINAL PROTOZOA OF FROGS AND TOADS. 239 
seen bifid condition of the caudal extremity is also not a 
constant feature. It owes its formation to the rigidity of 
the skeletal rods and the mobility of the cytoplasm in which 
they are imbedded. 
I have never seen anything corresponding with the undula- 
ting processes described by Stein. 
So far I have described the structure of adult individuals 
only. But in addition to these there are usually to be 
found a certain number of small forms. Many of these are 
exceedingly minute—not reaching a greater length than 
2-3 »—and are of a simpler structure than the fully grown 
animals. Even in the smallest forms, however, when it is 
possible to make an accurate count of the flagella, there are 
always eight present. But some of the tiniest organisms 
appear to have only one axostyle (see fig. 52, Pl. 5). Stein 
has figured the young form with four flagella and one 
axostyle. 
The shape of the smallest individuals is more rounded than 
that of adults. It is the nuclear apparatus, however, which 
shows the greatest differences. In the smallest forms (see 
fig. 32) the nucleus consists of a few loosely packed chromatin 
granules, and all the anterior flagella appear to be rooted in 
it. At other times the nucleus has a distinct karyosomic 
granule, and the flagella arise from minute basal granules on 
the periphery (see fig. 35). Later stages show a gradual 
transition to the bilobed nucleus of the adult (fig. 34), and 
many very small animals appear—as far as details can be 
made out—to be identical with adult individuals (fig. 35). 
‘he origin of these small forms is still unknown to me. 
Movements.—When freshly removed from their host 
these animals display a remarkable degree of activity. They 
move at such a pace that it is quite impossible to make out 
anything of their structure as they dart across the field of 
the microscope—a mere dot of protoplasm surrounded by a 
blur of flagella. After a short time, however, they slow 
down, and one is able to watch their movements with ease. 
