author's abstkact of this paper issued 

 by the bibliographic service, may 23 



AN EXPERIMENTAL STUDY ON GLOCHIDIA AND 

 THE FACTORS UNDERLYING ENCYSTMENT^ 



LESLIE B. AREY 



Anatomical Laboratory, Northwestern University Medical School 



THREE PLATES (FIFTEEN FIGXJREs) 



CONTENTS 



I. Introductory 463 



II. The glochidium 464 



A. Anatomy 464 



1. Hooked glochidia 464 



2. Hookless glochidia 465 



3. Axe-head glochidia 467 



B. Natural history 467 



III. Experimental 470 



A. Tactile excitation 470 



B. Photic excitation 477 



C. Thermal excitation 477 



D. Other modes of excitation 478 



E. Chemical excitation 479 



Chemical excitation in nature 484 



IV. The mechanism of encystment 487 



V. Summary 490 



VI. Literature cited 492 



I. INTRODUCTORY 



The young of fresh-water mussels pass the early stages of 

 development within the marsupial gill pouches of the female. 

 Here they progress to a simple, bivalved, larval form, the glo- 

 chidium, once believed to be a distinct animal parasite and 

 hence for a time termed Glochidium parasiticum. In reality, 

 the glochidia are eventually discharged from the gills and settle 

 to the bottom. Further development is conditional upon chance 

 attachment to the gills or fins of appropriate fishes in whose 

 tissues they become encysted, and, as virtual ectoparasites, begin 

 their metamorphosis. After such a period of parasitism, the 



1 Contribution no. 78, Jan. 5, 1920. 



463 



