FACTORS INVOLVED IN THE ATROPHY OF THE 

 ORGANS OF THE LARVAL FROG. 



WITHROW MORSE. i 



From the Nelson Morris Memorial Institute for Medical Research of the 

 Michael Reese Hospital, Chicago. 



PRELIMINARY. 



Throughout the two great branches of the organic realm, in- 

 stances are presented where persons, organs or tissues or cells 

 themselves undergo retrogressive changes. 2 In the plant king- 

 dom, we have the familiar elimination of stems, leaves and other 

 parts of the individual, upon the approach of untoward condi- 

 tions. In the animal series, we are enabled to identify an anal- 

 ogous process in the protozoa where, in Amoeba the ephemeral 

 pseudopodia are constantly being absorbed into the protoplasmic 

 mass proper; in the species of Actinophrys, where this process of 

 absorption is delayed permanently or at infrequent intervals; in 

 the genus Trypanosoma, where the undulating membrane be- 

 comes absorbed under certain conditions. Similar phenomena 

 are observed in the sponges where Maas's studies have shown that 

 hitherto highly differentiated cells become reduced to a mgre 

 typical and fundamental cell-form, the amoebocyte. In the 

 Ccelenterata we find the hydranths of Tubularw (i) and of other 

 species either absorbed or eliminated ^n toto, while in Renilla 

 Wilson has described a degeneration of the polyp. The "brown 

 bodies" of the Bryozoa represent degenerated individuals. In 

 brachiopods, during the stages of fixation there is present an 

 extensive degeneration of parts resembling in a superficial way 

 the various changes undergone by the larvae of the ascidians. 

 In Sacculina we have, facile princeps, this property of involution. 

 Even amongst the vertebrates we find instances of important 

 degenerations of a natural sort, as in the fish Fierasfer where 

 Bykowski and Nusbaum discovered extensive degeneration proc- 

 esses when the fish became parasitic. 



1 In order to avoid confusion, the author's name will be used henceforth as in 

 the title of this paper. 



2 Compare Child, C. M., "Senescence and Rejuvenescence." Chicago, 1915. 



149 



