W. 15. DWIGIIT. 131-(101) 



older ganoids with, vertebrated (orheterocercal) tails, are 

 inferior to the later in which the tails are not vertebra- 

 ted, (or homocercal). As the young of a frog, (a tadpole) 

 has the tail and form of a salamandrian, therefore the 

 salamandrians are inferior to frogs. As the number of 

 segments in the young of insects, often exceed much 

 that of the adult, therefore species of adult animals in 

 which there is an excessive number of segments, (beyond 

 the typical number), have in this a mark of inferiority." 



To the above illustrations of the applications of this 

 law, I may add two others. Ascidians of the solitary 

 type are globular animals of the sea-shore, generally 

 classed among molluscs, enclosed in a thick- walled sac. 

 One form of ascidians however, the appendicularia, in- 

 stead- of being simply globular, like the rest, has an 

 elongated appendage, and resembles a tadpole in shape. 

 Which is the higher form % Observation has shown that 

 the typical globular ascidians, in their embryo stage, 

 have the tadpole form of the appendicularia, losing it 

 when nearing maturity. The appendicularia has been 

 therefore arrested as it were, and fixed in its larval stage, 

 and is consequently the inferior form. Again, among 

 echinoderms, there are the crinoids, that once swarmed 

 in the sea but are now almost extinct, while to-day this 

 class is represented by star-fishes, sea-urchins and holo- 

 thurians. The latter are all stemless, while the crinoid 

 is like a. star-fish fixed to the rocks by a long stem. Which 

 is the lower in rank \ The larval forms of stemless echi- 

 noderms show the presence of a stem which drops off at 

 a later and higher stage. Therefore Xh% crinoid is a form 

 inferior to all the others. It is interesting to note that 

 the same conclusion is reached by the application of two 

 other criteria of rank, hereafter to be mentioned. 



Generalizations are always dangerous to truth, if car- 

 ried too far. So the grand principle above stated, must 

 be applied with caution, and with full recognition of 

 the fact, that it has its exceptions. Of these I may men- 

 tion the following : 



In the embryo of the mysticete or whalebone whales, 

 teeth are present. These are afterwards, (before birth) 

 absorbed into the gums, and in the adult, plates of 

 fringed whalebone take the place of teeth in the upper 

 jaw. It would be evidently absurd so to apply the above 



