Ityatt.J 110 [Aprils, 
to describe the number of cycles observed. I'liiis the am monoids 
are polycyclic, tlie Arietidae are decacycHc, the genu's C\)roniceras 
is ail incomplete monocycle. 
It is not necessary to defend these terms before students of 
bioplastology : they will be tested and if convenient adopted. 
For the benefit of others it may be mentioned that the cycle is of 
all degrees of development in ontogeny. Thus, Tnsecta are apt 
to stop at the ephebic stage and in many other animals there is a 
similar limitation. On the other hand there may be the most 
unexpected development of the cycle. Thus, Podocoryne starting 
from the hydroid stage passes through a permanent colonial 
stage built up by budding which gives rise by secondary buds to 
independent medusae. The life of an independent medusoid bud 
ends with a paragerontic substage in which tlie veil is destroyed, 
the bell is partially resorbed and turned back together with the 
tentacles, and the proboscis is left naked and projecting. In this 
condition the old of Podocoryne is similar to the hydroid with 
which the colony began. This gerontic transformation has been 
observed by Dujardin in Cladonema and Syncoryue, by Hincks 
in Podocoryne and Syncoryne, and by Gosse in Tunis. ^ 
Man is not completely ontocyclic but makes a close approach 
to this in the loss of the hair, teeth, and proportions and shape of 
the body ; and certainly in some parts, as in the mandible 
described above, there is sometimes a completed cycle. 
What the limits of the ontocycle may be has not yet been 
ascertained, but so far as the facts are known, it would appear to 
be coincident vvith the limits of agamic reproduction or in other 
words with the limits of the growth of one autotemnon or of one 
ovum after conjugation by fission, and includes all agamic genera- 
tions produced bj^ division or by budding. 
The act of self fission is similar whether it takes place for a 
certain cycle among Protozoa or Metazoa under purely organic 
conditions or follows upon the conjugation of two zoons, and is 
due to the rejuvenation caused by the union of the nuclear 
elements of their bodies as among Protozoa or the more differ- 
entiated generative cells of the Metazoa. Under all conditions 
the cells divide in obedience to the laws of growth, and whether 
1 Dujardin, Anu. sci. nat., ser. 3, v. 4, p. 257-281, 18-to: Hincks, British hydroid 
zoophytes, v. 1, p. xxviii, 1868. 
