6 HARLEY N. GOULD 



torina, inhabited by the little hermit crab Eupagurus longi- 

 carpus, are found 'dwarf plana,' They are exactly like the 

 typical form but average only one-fifteenth the volume, have 

 fewer cells in their tissues, and lay a little more than one-third 

 the number of eggs. Their tissue cells and eggs are, however, 

 r.s large as those of the typical form. The organs only are 

 smaller. When these dwarfs are removed to a situation where 

 they have plenty of room to grow, their size increases far beyond 

 its former limits. The conclusion is that they are a 'physio- 

 logical variety' merely, their smaller size being due to a stop- 

 page of cell growth and division by the cramping of the 

 environment. 



From the writer's own experience it may be added that every 

 possible gradation may be found between the dwarfs and the 

 typical forms. Comparison can be made between adult females 

 only, for up to the adult female phase the sexual condition, 

 whether immature, male or transitional, has little relation to 

 the age and size. The females differ most markedly in size 

 even in the largest shells, and this variation is not all to be 

 ascribed to age differences, as the lines of growth show; there 

 are instances of cramping environment here as well as with the 

 smaller hermits. When the dwarfed individuals are trans- 

 ferred to a fingexbowl or aquarium one observes with surprise 

 how quickly they extend the mantle and begin to deposit shell 

 in a thin layer. The thin rim of new shell may be evident the 

 day following the transfer. 



Now such an increase in growth rate may be inaugurated not 

 only in dwarfed females, but in almost any of the small Crepi- 

 dulas having a thick and convex shell and living in the crowded 

 colonies. The new growth is most striking when they are 

 placed in glass dishes of sea water with a perfectly smooth sur- 

 face and nothing to interfere with the extension of the mantle. 

 It is evident that in all crowded colonies there is a suppression 

 of growth of the animals because they do not have unlimited 

 surface on which to extend the mantle. 



It has been found that the small Crepidulas kept in the in- 

 land vivarium during the winter have a very limited growth 



