Introduction to Animal Morphology. 5 



nor has it any properties other than those of any other 

 particle of vigorous protoplasm.* It may be granular, 

 sometimes vacuolated [Rollcft), and often has a denser 

 spot within it called the nucleolus. Each independent 

 protoplasm mass is named a plastide ; a plastide with 

 no nucleus is a cytode ; a nucleated plastide is a cell ; 

 a naked cytode is called a gymnocytode ; one invested 

 by a membrane is a lepocytode ; a naked cell is a 

 gymnocyte (monoplast Sharpey) ; one with a cell- 

 membrane is a lepocyte [Hceckel). The largest single 

 cells are the myeloplaxes of growing bones and the 

 muscle cells of Nematodes. 



Plastides multiply by gemmation, a bud arising as 

 a small process from a parent cell, then enlarging and 

 becoming detached ; by fission, each splitting into two 

 or more nearly equal parts — in this process the nucleus 

 may or may not take partf ; — by free cell formation, 

 nuclei arising in a mass of protoplasm, and around 

 each an area of protoplasm becoming isolated by 

 the differentiation of cell-membranes — this occurs in 

 developing embryos ; — by endogenous formation, as 

 shown by Weissmann in the eggs of Diptera, and by 

 E. Va7i Beiieden in the formation of the nucleus in 

 Pseudofilaria of Gregarina gigantea.:}: It occurs pa- 

 thologically in tumours. 



* Gegenbaur states that the nucleus differs from the surrounding pro- 

 toplasm by being non-contractile, but Bottcher has demonstrated that a 

 free nucleus or a nucleus removed from a cell contracts actively. Neumann 

 describes the nucleus as showing motions in dying cells. Free nuclei may 

 exist in masses of protoplasm. 



t Remak and Weiss have seen cells divide while the nucleus was ad- 

 herent to one side. The same has been noticed by many other observers. 



X The multiplication of cells in cartilage, some tumours or ova, is 

 sometimes regarded as of this kind, but in reality it is more likely a con- 

 9ealed form of fission. The instance given by BtM of the formation of 



