FRONTAL APPENDAGE——-PHYLLOPOD CRUSTACEAN (awe 
appendage. With the contraction of the large flexor muscle 
the blood is forced backward through the sinuses into the large 
sinus with which they connect. As the muscle of the appendage 
is large the structure might be used as a strong clasping ap- 
pendage. It is hard to understand, however, just how this 
median structure might thus be used, if copulation (which has 
not yet been observed in Thamnocephalus platyurus) takes 
place in a way similar to that in which it occurs in Artemia 
gracilis Verrill, as figured by Packard (’78, fig. 17). If copu- 
lation does take place in a similar manner and the appendage 
does not function as an additional clasping organ then it is pos- 
sible that the appendage is used as an organ for stroking the 
female on the back while in coitu. 
In conclusion, it may be stated that the function of a sensory 
organ is apparently eliminated by the lack of nerves or sensory 
cells in the structure. The large muscles would indicate that 
it is very likely used for seizing and holding, which would put 
it in the category of a purely copulatory structure. 
Whether the function is that of a clasping or stroking organ 
must remain an open question until the animals are more 
closely observed in the field and actually seen in the process of 
copulation. 
The writer is indebted to Prof. Max M. Ellis for the material 
used in this study, as well as for suggestions in the preparation 
of the paper. 
University of Colorado 
