Changes in the Life-cycle B17 
‘tadpole is prevented by keeping the animals in cold water, the 
hind legs may continue to grow larger and their bones become 
harder. The long spiral intestine shortens, as it does when the 
tadpole changes into the frog, but the sexual organs do not 
mature. 
How extensive the phenomenon of neotenia occurs in other 
-amphibia is not known. It has been suggested that forms like 
Necturus, that always have external gills, do not representmore 
primitive members of the group, but are neotenic species that 
never undergo a metamorphosis, and become sexually mature 
in the larval stage. Jn other groups of the animal kingdom the 
same phenomenon occurs, according to some zodlogists. Thus 
it has been suggested that the rotifers represent the sexually 
mature trochophore larval stage of the annelids, which has lost 
its power to transform. Similarly, Appendicularia has been 
supposed to be a sexually mature larval form of an ascidian, 
. and it has been suspected that even Amphioxus may be a neo- 
tenic form. 
Boas has brought together many cases in which special or- 
gans remain in a lower stage of development, while other organs 
in the same animal undergo the characteristic transformation. 
Thus we seem to have three forms of neotenia: one in which the 
body remains at a lower stage and the sexual organs ripen; 
another in which some of the organs advance (as in the tadpole), 
but sexual maturity does not supervene; and third, those in 
which some organs fail to develop at the time of sexual maturity. 
A case that appears to be a parallel one in some aspects exists 
in the white ants according to Grassi. The members of the 
colony consist of a royal couple, workers, soldiers, and young. 
If one of the royal pair is removed, a royal substitute form is 
reared, either male or female, according to which is needed. 
If both royal individuals are removed, two royal substitutes are 
reared. Grassi has shown experimentally that this occurs, but 
the way in which the transformation is effected was not deter- 
mined, although he thinks that the amount or the kind of food, 
given to the young determines the result. The young appear 
