88 SCIENCE PROGRESS. 



been found suggestive of a morphologically paired nature, 

 has recently become the centre of a renewed interest, 

 in the assertion 90 that it appears early in development 

 as one of two pairs of bilaterally symmetrical organs, 

 serially recurrent with the paired eyes. And the far-reach- 

 ing significance of this (if true) is none the less interesting, 

 in view of the long-recognised suggestion of a paired 

 nature by the median Crustacean eye, and the fact of the 

 persistence of this in adults of even the Decapod group. 91 



On all hands one meets with reform by progres- 

 sive development along continuous lines of inquiry, 

 with sure indications that true progress in science 

 does not march by leaps and bounds, but by an evolu- 

 tionary process of gradual unfolding, under which each 

 step in advance bears the impress of those immediately 

 antecedent to it. Future historians will unmistakably 

 have to chronicle error due to the too exclusive devotion 

 to pure embryology, which so unconsciously lends itself 

 to over-generalisation, and to the attempt to force the 

 extinct into a too rigid classification with the living. 

 Experience shows that whole groups of animals have 

 dropped out of existence, and that the exclusive study 

 of the embryology of animals, like that " of ana- 

 tomy " of plants, lends itself to the accumulation of 

 meaningless detail, as does that of mere histology to 

 a sort of laborious idleness. The study of ontogenetic 

 development must be pursued hand in hand with that of 

 adult of anatomy and palaeontology 92 — gross morphology if 

 anything leading the way — the three being as fully inter- 

 dependent as are the allied pursuits of histology and 

 experimental physiology. It cannot be denied that, for 

 the bare want of appreciation of this principle, much that 

 has been written within the period which we have named 

 has become, in its own time, valueless ; and it is only by 

 rigid adherence to this that the study of animal morphol- 

 ogy can retain that honoured position among the sciences 

 of which its devotees are justly proud. 



