[Illustration: FIG. 60. _Stentor rœselii_, trumpet-animalcule. Process of division. _wsp_, ciliated spiral leading to the mouth (_m_); _cv_, contractile vacuole. _A_, in preparation for division, the nucleus (_k_) has coalesced into a long twisted band. _B_, a second ciliated spiral (_wsp´_) has begun to be formed; the nucleus (_k_) is contracted. _C_, just before the constricting off of the two daughter-Stentors. Magnified about 400 times. After Stein.] Now that we have become familiar with these facts it will no longer surprise us to learn that the reproduction of unicellular animals does not always depend on _equal_ division, but that unequal spontaneous divisions are also possible, so that one or several smaller portions of the cell-body, containing a portion of the cell-nucleus, can separate off from the mother-animal. This occurs especially among the suctorial Infusorians or Acinetæ. In relation to the phenomena of inheritance the problem raised by the equal division of the Infusorians repeats itself, and it is in no way affected by the fact that equal division can take place several times, or many times in succession, so that from one animal a large number of small pieces of the same size may be produced in rapid succession. The characteristic marks of the mother-animal are not infrequently lost sight of, wholly or partially, when this occurs, and the divided portions seem to consist of a homogeneous cell-body and nucleus; but they possess the power of regenerating themselves, or of developing, if the expression be preferred, into animals similar to the maternal-organism. Such divided portions might very well be called germs, only it must not be forgotten that the relation of the mother-animal to these germs is a different one from that of a higher animal or plant to its germ-cells; the unicellular animal breaks up by continued division into these 'germs,' while the Metazoon continues its individual existence unimpaired by the production of its germ-cells.