132 ERNEST WAHEEN. 



the result of an unseen architecture in the cytoplasm^ which 

 is only rendered visible by the physiological disturbance 

 induced by the adverse stimuli. In many animal diseases 

 such a distui'bance may arise through the presence of toxins 

 produced by parasitic bacteria, etc., which may be far distant 

 from the actual place where cellular degeneration is occurring 

 and eruptions and sores of characteristic appearance and 

 shape are being formed. Nevertheless, characteristic diseases 

 are not necessarily due to such poisons. Unfavourable 

 stimuli of various nature, such as excessive heat, chemical 

 rays of light, friction, undue pressure, etc., may produce 

 a characteristic reaction in the protoplasm of the cells, 

 and degeneration changes may set in and result in the pro- 

 duction of visible effects, such as hyperpigmented spots, 

 freckles, running sores, etc., entailing the death of cell- 

 elements. 



Degeneration changes may be confined to a particular 

 portion of a cell, as is seen in text-fig. 6, h, where a sym- 

 metrically placed pigmented chamber occurs in each of two 

 contiguous endoderm cells. Also, in text-fig. 4, a, c, may be 

 seen the formation of branching streaks of degenerated 

 protoplasm extending through portions of the living cyto- 

 plasm of a considerable number of cells which are in contact 

 with one another. Here is evidence of the unseen archi- 

 tecture of the cell, referred to above, since the affected 

 portions of the cytoplasm of the cell must be in a different 

 physiological or physical condition from the other portions of 

 the cytoplasm which are not so affected. 



It is interesting to note the differences in the reactions 

 which occur in the different species of hydroids when acted 

 upon by what are presumably the same adverse stimuli ; 

 different kinds of cells may be affected and the characteristic 

 shape and general facies of the degenerated areas differ to 

 some extent in every species examined. 



The reaction to these stimuli appears to be a definite one 

 for each species, and does not seem to vary from time to time, 

 although the individuals affected cannot always be in the 



