AND ITS BIOLOGICAL SIGNIFICANCE. 



327 



in the left one. In the last five or six species named the rudimentary right toe has 

 usually been classed with the substyles, though it can as a matter of fact be recog- 

 nized when a comparison of a series of species is made. Finally, there are certain 



rsu muc. 



■piQ. G. — Toes of a number of species of Rattulidae, viewed from the dorsodextral side, showing stages in reduction 

 of the right toe (original). Abbreviations: dg.dx., right toe; gl.muc., mucous gland; rsv.muc., mucous 

 reservoir. 

 1, Diurella tigrisMiiller; 2, Diurella stylata Eyferth; 3, Diurella brachyuraGosse; 4, Diurella porcellus Gosse; 



5, Diurella insignis Herrick; 6, Diurella tenuior Gosse; 7, Rattulus gracilis Tessin; 8, Rattulus lophoessus Gosse; 



9, Rattulus elongatus Gosse; 10, Rattulus longiseta Schrank; 11, Rattulus scipio Gosse; 12, Rattulus carinatus 



Lamarck; 13, Rattulus multicrinis Kellicott; 14, Rattulus pusillus Lauterborn; 15, Rattulus bicristatus Gosse 



(proximal part of toe). 



species, as Rattulus bicristatus Gosse (15), in which it is difficult or impossible to 

 distinguish between the rudimentary right toe and the substyles. 



