CONTROL OF ASYMMETRY IN HYDROIDES 929 
AK 
) 
YY yy 
/ Lf 
) 
/ 
Ss) 
\ \\ 
S 
VAY 
Hy 
Vy Yh? 
Vif 
WOH WW \ 
Uy 
S 
Yi 
4, 
LS 
\ 
i 
/ 
SMH JL I ff / 
/ Le ff f, / 
: / Uy, tf, 
7 ci S4i tt 
LOBES 
B 
Fig.1 Hydroides dianthus. A, dorsal view of right-handed specimen, showing 
relations of parts. Ends of branchiae and functional operculum not given (6); 
B,C, diagrams of anterior surface of head of left-handed and right-handed speci- 
mens (X6); D, branchia viewed from inner surface (X25); #, rudimentary oper- 
culum (X 30). fF, functional operculum (X 30). 
The process is very similar to the reversal of the two chelae 
in Alpheus as described by Przibram (’01 to ’07), Wilson (’08), 
Zeleny (’05) and Stockard (10). In Alpheus there is a larger so- 
called ‘snapping’ chela on one side of the body and a smaller 
‘cutting’ chela on the other side. These chelae differ from each 
other both in size and in structure. When the snapping chela is 
