390 THE POPULAR SCIENCE MONTHLY, 



retrogressive while the other sex remains structurally fully developed. 

 Such a case is illustrated by the males of those remarkable organisms, 

 the Motif era^ or " wheel-animalcules " (Fig. 19). These minute creat- 

 ures, inhabiting our fresh waters, may be desiccated and dried, and 

 revived, on the application of moisture, many times in succession. 

 But in their ordinary existence, and in the details of their structure, 

 the " wheel-animalcules " present details equally interesting with their 

 exhibition of " potential vitality." The female animalcules possess a 

 complete digestive system, a set of water vessels, a nervous ganglio;n, 

 and other belongings ; but their partners are decidedly inferior creat- 

 ures, since their digestive system becomes totally abortive, while in 

 size the males are likewise far excelled by the lady rotifers. How this 

 degeneration and disappearance of digestive apparatus and the inferi- 

 ority of size have been produced in the male rotifers may be a matter 

 regarding which difference of opinion will certainly exist in biological 

 minds. The fact that retrogression is here illustrated, however, can 

 not be questioned. It may also be added that, in all probability, the 

 extreme development of the function of perpetuating the species and 

 the extraordinary fertility of production witnessed in these animal- 

 cules, may satisfactorily account for the abrogation of digestion in 

 favor of reproduction. Thus, to the other causes of degeneration in 

 animal life and structure, we may append that which takes origin from 

 the extreme or excessive development of one function over another. 

 Physiological development in one direction, overstepping the natural 

 and ordinary limits, runs concurrently with destruction of life's equi- 

 librium, and naturally tends to produce degeneration and simj^lification 

 of other organs and other duties of life. 



How far the theory of degeneration we have thus briefly discussed 

 may be applied in explanation of the peculiarities of animal structure, 

 remains as a task for the future of biology to satisfactorily determine. 

 Possibly the corrections which the future of every hypothesis carries 

 with it may be many and sweeping. The deductions and inferences 

 we extract from a study of degeneration to-day may perchance be 

 falsified by the higher and newer views of the to-morrow of biological 

 science. But enough has been said to show that, even in a cursory 

 review of the doctrine of degeneration and retrogression, many phases 

 of living histories become theoretically plain ; and it argues hopefully 

 for the correctness and value of the doctrine before us that it has, so 

 far as it has been logically pursued, fitted compactly and harmoniously 

 enough with ascertained facts and with received views of the origin 

 of animals and plants. That higher forms of life than the sea-squirt 

 and insect race are by no means exempt from the influence of retro- 

 gressive change is an observation worth noting at the close of our 

 researches. We know, for instance, of lowly structures in shell-fish 

 life appearing in the midst of highly organized frames. A mussel, 

 a cockle, or an oyster, whose early development runs in parallel lines 



