liS8/).] MR. J. B. SUTTON ON HYPERTROPHY. 443 



of the succeeding teeth (canines and premolars in rodents) became 

 reduced to a minimum, so that diminished usaj;e would also tend 

 to lower the vascular sn|)|)ly : thus the two factors, diminished 

 function and diversion of nutrient fluid, have brouolit about extreme 

 atrophy and, in many cases, total disappearance of teeth. 



Numberless other instances might be quoted, indeed they must 

 readily suggest themselves to any mind that carefully meditates on 

 the matter. Tiie cases of MesopJodon and Monodori seem to me 

 to be very extreme examples of this remarkable process. 



I propose now to consider some examples of hypertrophy as thev 

 affect the reproductive organs ; and shall adduce evidence to show 

 that this process is one of the proliable causes of division into sexes. 

 Many anatomists are of o|)inion that hermaphroditism is tiie primitive 

 condition of the sexual organs. 



Hermaphrodites are found in every group of the animal king- 

 dom, but, except in some of the lowest forms (such as Qtenophora 

 and Chrysaora) among the Coelenterata, self-fertilization appears to be 

 wholly exceptional, and in those forms in whicli it occurs the entire 

 process is of very simple character. The rule in hermaphrodites 

 appears to be this : — The male organs in one animal are used to 

 impregnate the female organs of another, or vice versa. Even in the 

 Cestoda, where there are arrangements favourable to self-impregna- 

 tion, we have no positive evidence that it takes place. 



From this arrangement it would easily come to pass that if one 

 animal used the male portions of its reproductive organs more freely 

 than the female parts, they would, as a result of increased function, 

 hypertrophy. 



In the first portion of this paper I emphasized tlie fact that any 

 marked degree of hypertropiiy in one organ nearly always leads to 

 dwarfing of the correlated organ or sets of organs ; hence in the 

 example considered, the female portions of the hermaphrodite organs 

 remain dwarfed or in statu quo. This peculiarity would in the 

 natural course of events be transmitted to the offspring, until at last 

 the differentiation attains such a high degree, that unless hyper- 

 trophy of one set of organs occurs in each individual, propagation is 

 impeded. Evidence on this point is afforded by the developmental 

 history (ontogeny) of any mammal. Whilst the two sets of repro- 

 ductive organs, male and female, up to a certain jioint maintain the 

 same degree of growth, it is impossible to determine the sex of the 

 embryo. As soon as one set begin to enlarge at a greater rate than 

 the other, the sex becomes pronounced. The remaining organs may 

 eventually disappear or merely exist in such a rudimentary condition 

 as to be discerned only by the most diligent search. 



Indeed this process has been observed to occur in a very complete 

 manner in a single group, the Myzostomida. Dr. L. von Graff, in 

 his " Report on the Myzostomida " collected during the voj'age of 

 the ^ Challenger,' has noted the following interesting facts. Some 

 species {Myzostomn tenuispinum, M. willemoesii, M. hiflator, and M. 

 mur7-ayi) are originally descended from androgynous forms in which 

 the organs of one sex have become gradually aborted ; for in Myzo- 



