METAMORPHOSIS OF LAMPSILIS L/EVISSIMUS. l8l 



form, broadly winged, and with "axe-head" glochidia still further 

 modified by the development of hooks. Capax has the same 

 type of glochidium, but what of the adult form (Figs. 4& and 4^)? 



In external shape capax and ventricosus are so closely alike 

 that it has sometimes been doubted if the two species were 

 properly separable. However, the species capax is now uni- 

 versally accepted, for the reason that capax is clearly distinguish- 

 able from ventricosus in: (i) the polished almost rayless character 

 of its epidermis, (2) the compressed form of the teeth, and (3) 

 in the relative thinness of its shell, w r hich is inclined to pinkness 

 in color of nacre. Now these, it is significant to remark, are all 

 characters of Icevissimus. In fact, (i) above is the most certain 

 means of distinguishing, l&vissimus from gracilis. 



If, then, we were to draw an inference from the glochidia as 

 to a relationship between Icevissimus, alatus and capax, there 

 would be strong corroborative evidence in the adult characters, 

 in spite of the fact that Icevissimus and capax are the two ex- 

 tremes in degree of inflation. The similar degree of inflation of 

 capax and ventricosus would offer only a striking instance of 

 convergence in one character. 



2. CHANGE OF FORM DURING PARASITISM. 



The change undergone by Lampsilis Icevissimus during para- 

 sitism is most striking. As a general rule, it has been held that 

 there is practically no growth in size during the period of para- 

 sitism simply a metamorphosis from glochidium to young mus- 

 sel in rudimentary form. Our observations show a notable 

 exception to this general rule. 



While examining the gills of a specimen of the sheep's-head, 

 Aplodinotus grunniens, several specimens of encysted glochidia 

 were found in an advanced stage of development. The infection 

 occurred in nature, so that the age of the mussels cannot be 

 stated. 



Figs. 5, 6 and 7 show not only the striking change in form, but 

 the enormous increase in size as well. Fig. 5 shows a specimen 

 in side view; the "axe-head" glochidium shell is evident, but 

 the mussel is now nearly circular in outline and several times 

 larger than the glochidium. The specimen shows considerable 



