232 
R. Ruggles Gates. 
Perhaps the most convincing of all cases for a Lamarckian 
interpretation of recapitulation is that of the parasitic Copepod, 
Achtheres ambloplitis , where as MacBride remarks, “we may almost 
say that the ancestor is known.” The adult is a parasite on the 
gills of the rock-bass, and is a sac-like organism devoid of all 
semblance of Copepod structure, yet the animal passes through a 
brief larval stage which anyone would recognize at once as 
representing a typical Copepodan genus. Whatever explanation 
applies to this remarkably clear case must also apply mutatis 
mutandis to the whole series of larval stages which represent the 
remoter ancestry in other organisms. We think this case furnishes 
one of the clearest evidences of the sharp contrast we are 
endeavouring to draw between recapitulatory and mutational, or in 
other words, between organismal and karyogenetic characters. Yet 
it is admitted that even in this Copepodid larva there are modifica¬ 
tions from the typical details of Copepod structure. But they 
follow the usual lines of diminution in size of the larva and 
consequent reduction in the number of metameric parts. Another 
factor which tends to obscure ancestral stages is the well-known 
principle of telescoping, or the earlier appearance of embryonic 
organs, which has been called heterochrony by Lankester, or 
tachygenesis by French writers (Perrier and Gravier, 1902), That 
embryonic and larval stages can also undergo special modifications 
of an adaptational nature is another well recognized principle which 
tends to obscure ancestral relationships. 
Many of the battles of recapitulation have been fought over the 
frog, so we may briefly examine his case. Some embryologists 
have gone so far as to deny any ancestral significance to the 
tadpole. While the other extreme view, that all larval characters 
of the frog have ancestral significance, is certainly disproved; yet 
the truth evidently lies in a recognition of the fact that in the 
tadpole as in most other larvae, there are some recapitulatory 
or palingenetic characters and some adaptational or coenogenetic 
characters. The obvious recapitulatory characters are the fish-like 
tail, gill arches and blood system. It seems impossible to avoid 
the conclusion that these were once terminal developmental stages, 
in the frog’s fish-ancestor. On the other hand Boulenger (1918) 
has pointed out that tadpoles have had an evolutionary history of 
their own and have developed special adaptational features. He 
enumerates (Boulenger 1897) “The horny beak and circular lip 
with its horny armature, the spiraculum, the enclosure of the fore- 
