136 THE INDUCTIONS OF BIOLOGY. 



mansions have an obscure if not a distinct axial structure. 

 The originally cellular units out of which higher organisms 

 are mainly built up, usually pass into shapes that are subordi 

 nated to lines rather than to points. And in the higher organ 

 isms, considered as wholes, an arrangement of parts in rela 

 tion to an axis is distinct and nearly universal. We see it in 

 the superior orders of Thallogens ; and in all the Acrogens, 

 Endogens, and Exogens. With few exceptions the Ccelente- 

 rata clearly exhibit it ; it is traceable, though less conspicu 

 ously, throughout the Mollusca; and the Annulosa and 

 Vertebrata uniformly show it with perfect definiteness. 



This kind of development, like the first kind, is of two 

 orders. The whole germ-product may arrange itself round 

 a single axis, or it may arrange itself round many axes ; the 

 structure may be uniaxlal or multiaxial. Each division of 

 the organic kingdom furnishes examples of both these or 

 ders. In such Fimgi as exhibit axial development at 

 all, we commonly see development round a single axis. Some 

 of the Algce, as the common tangle, show us this arrange 

 ment. And of the higher plants, many Endogens and 

 small Exogens are uniaxial. Of animals, the advanced are 

 without exception in this category. There is no known ver 

 tebrate in which the whole of the germ-product is not subor 

 dinated to a single axis. In the more fully-organized Annu 

 losa, the like is almost universal ; as it is also in the superior 

 orders of Mollusca. Multiaxial development occurs 

 in most of the plants we are familiar with every branch of 

 a shrub or tree being an independent axis. But while in the 

 vegetal kingdom, multiaxial development prevails among the 

 highest types; in the animal kingdom, it prevails only among- 

 the lowest types. It is extremely general, if not universal, 

 among the Ceelenterata ; it is characteristic of the Mollus- 

 coida ; among Molluscs the compound Ascidians exhibit it ; 

 and it is seen, though under another form, in the inferior 

 Annulosa. 



Development that is axial, like development that is central, 



