490 LESLIE B. AREY 



the fish, the normal inhibition, whatever it may be, that causes 

 the heahng process to stop at the appropriate point, is lost. 

 In this sense, typical encystment depends on the integrity of the 

 gill as a normal living entity attached to the body. 



A reciprocal experiment was made to test whether the glo- 

 chidium takes any part in stimulating cyst formation by a chem- 

 ical or vital influence: 



Lampsilis luteola glochidia were ground to a paste. A gill filament of 

 the bass, Micropterus salmoides, was placed in a drop of this, another 

 in a drop of tap-water for a control, and both set in a moist chamber. 

 No positive results were gained that could be attributed to the glochidial 

 mass. In some cases both the experimental gill and the control showed 

 general surface proliferation to form investments, but the responses 

 were inconstant and uneven; nevertheless, this phenomenon, by itself, 

 deserves further attention. 



Such experiments cannot be regarded as furnishing evidence 

 that the glochidia induce cyst proliferation in any but a mechani- 

 cal fashion. Moreover, Needham and Lloyd ('16) are not precise 

 when they write (p. 291) : ''Whether it be the mussel that reacts 

 to only a certain kind of fish substance, or the fish that reacts to 

 form a cyst only for a certain glochidial stimulus is not known;" 

 for not only do glochidia attach to any fish with appropriate 

 configuration of parts, but also a cyst is usually formed in such 

 instances; what does happen when a glochidium attaches to a 

 non-host or immune host is the early loss of the cyst and contents 

 by sloughing (Reuling, '19). 



V. SUMMARY 



The only response to excitation that glochidia can express is 

 a closure of the valves by contraction of the adductor muscle. 



Glochidia of all types respond promptly and vigorously to 

 appropriate tactile stimulation. The half of the mantle nearer 

 the hinge possesses the keenest sensitivity. This may be useful 

 by insuring a more liberal bite of host tissue. 



Tactile activation is probably mediated normally through the 

 hair cells of the mantle, although closure can be accomplished 

 without directly touching these. 



