io Introduction to Animal Morphology. 



higher heat, and Calvert has shown the same regarding 

 Vibriones. Many of these experiments indicate the 

 existence of some hidden fallacy, as the organisms 

 produced are by no means the lowest, but compara- 

 tively complex. The hypothesis that every protoplasm 

 mass is the produce of a pre-existing protoplasm is 

 known as Biogenesis or Panspermism. 



CHAPTER II. 



GENERAL MORPHOLOGY. 



PLASTIDES continuously grouped form tissues, which 

 vary according to the nature of their components and 

 of their intercellular substance. The fusion of cells 

 within a common investment constitutes the simplest 

 tissue (Cytocormi, possibly the condition in some 

 Protozoa). Continuous groups of similar cells (each 

 with its own wall) constitute homoplastic tissues, as 

 simple cartilage, hair, cuticle, &c. ; if the cells be dis- 

 similar, or if the intercellular substance be abundant, 

 they form a heteroplastic tissue,* as connective tissue, 

 muscle, nerve, &c. Each set of heteroplasts may 

 make an entire animal (as in some Radiolaria), or in 

 the body of a more complex animal they form an 

 organ-system (as the dermal, skeletal, muscular, &c.), 

 and these systems are part of a more complex 

 functional grouping or apparatus, as the locomotory 

 (of the muscular and osseous systems), circulatory, 

 respiratory, &c. The grouping of heteroplastic organs 



* Heteroplasty is the method whereby physiological divis.'on of labour is 

 accomplished. 



