45, 
All organs, functionless in the adult but functional in the early on- 
togeny, develop in the normal way. Organs no longer functional at any 
time dwindle all along the line of development. In Typhlogobius, where 
the eye is functional in the young, it develops in full size in the embryo, 
and it is not till late in life that degeneration is noticeable. In Ambly- 
opsis, on the other hand, where the eye has not been functional at any 
period of ontogeny for many generations, where the eye of both young 
and adult lost their functions on entering the caves and where degenera- 
tion begins at an early period and continues till death, the degenerate con- 
dition has reached the early stages of the embryo. It is only during the 
first few hours that the eye gives promise of becoming anything more 
than it eventually does become. The degree of degeneration of an organ 
can be measured as readily by the stage in ontogeny when the degenera- 
tion becomes noticeable as by the structure in the adult. The greater the 
degeneration the further back in the ontogeny the degenerate condition 
becomes apparent, unless, as stated above, the organ is of use at some 
time in ontogeny. It is evident that an organ in the process of being per- 
fected by selection may be crowded into the early stages of ontogeny by 
post selection. Evidently the degenerate condition is not crowded back 
for the same reason. How it is crowded back I am unable to say. A 
satisfactory explanation of this will also be a satisfactory explanation of 
the process by which individually acquired cnaracteristics are enabled to 
appear in the next generation. The facts, which are patent, have been 
formulated by Hyatt in his law of tachygenesis (Hyatt IX). 
Cessation of development takes place only in so far as the number of 
cell divisions are concerned. The number of cell generations produced 
being continually smaller, result in an organ as a consequence also 
smaller. In this sense we have a cessation of development (cell division, 
not morphogenic development) in ever earlier stages. That there is an 
actual retardation of development is evident from Amblyopsis and Typh- 
lichthys in which the eye has not reached its final form when the fish are 
35 mm. long. 
Histogenic development is a prolonged process and ontogenic degen- 
eration is still operative, at least in Amblyopsis. 
Degeneration in the individual is not the result of the ingrowth of 
connective tissue cells as far as I can determine. It is rather a process 
of starving, of shriveling or resorption of parts. 
