66 THE MITOCHONDRIAL CONSTITUENTS OF PROTOPLASM. 



V. MORPHOLOGY. 



MORPHOLOGY IN ORGANISMS. 



We rarely meet with forms which possess mitochondria of pecuhar or dis- 

 tinctive morphology. In multicellular animals and plants, high up in the scale, 

 in which there is considerable division of labor among their constituent parts, all 

 forms of mitochondria are represented, though some may predominate. In uni- 

 cellular organisms, on the other hand, the mitochondria are sometimes granular, 

 sometimes filamentous, sometimes large and sometimes tiny, depending upon con- 

 ditions which are wholly obscure. Frequently we meet with all forms within the 

 compass of a single cell. Obviously they can never be used in a taxonomic way, 

 like the chromosomes, to distinguish between nearly related species. This is equally 

 true for animals and for plants. 



MORPHOLOGY IN TISSUES. 



The several tissues of the higher plants and animals possess mitochondria 

 of characteristic form; that is to say, in some of them filaments predominate, in 

 others granules, and so on, but in similar tissues of different animals they are much 

 the same. For instance, I find it difficult, even in the different classes of verte- 

 brates, to distinguish the spinal ganglion cells from each other on the basis of their 

 mitochondrial content alone. The mitochondria in the liver, pancreas, lung, 

 prostate, and other organs are characterized by the predominance of some definite 

 form, granule, rod, or filament in all nearly related animals. This general constancy 

 of mitochondria, where the function is similar, is, I think, of considerable importance, 

 because it must surely indicate that their morphology is a fundamental property 

 ingrained in the very organization of the cell in phylogeny and that it is not always 

 a passing trivial affair which varies from moment to moment. 



Mitochondria are for the most part filamentous in certain nerve-cells (plate 1 , 

 fig. 4), in gland-cells (plate 1, fig. 9), and others, as well as in most of the tissues of the 

 developing embryos of all forms. Indeed, filamentous mitochondria are among the 

 most common met with anywhere. The average length of the filaments varies in 

 different tissues : they are perhaps longest in secreting cells, like the pancreas, where 

 they may attain a length of 10 to 12 ii. Their diameter also varies (0.05 to 0.2 n) 

 in different localities, but in individual cells of the same tissue it is astonishingly 

 uniform. Within a single cell the length is variable and the breadth uniform. 

 They may be straight, curved, or even twisted, depending upon their surroundings. 

 They do not begin to taper toward their extremities, which end abruptly and 

 evenly. Sometimes their ends are somewhat swollen. 



Filaments are never produced from granules through the action of the fixati\-e. 

 Some think that they are formed, in the living tissue, by linear coalescence of 

 individual granules; others, that they arise from single granules through growth by 

 accretion. Certain it is that in those cells where filaments are abundant all transi- 

 tions may be seen between them and granules, while filaments are often totally 

 absent in cells with granular mitochondria. 



