Septembee i, 1914] 



SCIENCE 



353 



appears to have some effect, as when the an- 

 tenna were cut between the first and second 

 segments nothing but a knot developed but 

 when the cut was made between the second and 

 third segments' a foot was regenerated. 



A. N. Caudell 



SPECIAL ARTICLES 



A SECOND CASE OP METAMORPHOSIS WITHOUT 

 PARASITISM IN THE UNIONIDjE ^ 



The discovery^ three years ago that the 

 species Strophitus edentulus (Say) passes 

 through its metamorphosis in the entire ab- 

 sence of parasitism placed that species in a 

 unique position among fresh-water mussels. 

 Since Leydig in 1866 solved the mystery as 

 to the post-embryonic development of the 

 Unionidag in the discovery that the glochidia 

 are parasitic on fishes, the announcement by 

 Lefevre and Curtis seems to have been the 

 first reported exception. 



Lefevre and Curtis^ in their investigations 

 into methods of propagation of fresh-water 

 mussels found that certain species of fish 

 are more susceptible than others to infection 

 by glochidia. In their operations a number of 

 species of mussel were employed, but the com- 

 mercially important species were chiefly eon- 

 fined to members of the subfamily Lampsilinae 

 Ortmann.* The fishes found adaptable to 

 infection were the common game fish of the 

 family Centrarchidae. The fishes which did 

 not take artificial infection were considered 

 by them examples of specific immunity to 

 infection by glochidia. 



Following the work of Lefevre and Curtis 

 considerable effort was made to carry through 

 artificial infections with mussels of the genus 

 Quadrula (Eafinesque, 1820) Agassiz, a group 

 economically important because of their heavy 

 shells. These attempts, employing the 



1 Printed by permission of the Commissioner of 

 Fisheries. 



2 Lefevre and Curtis, Science, Vol. 33, pp. 863- 

 865, 1911. 



3 Bulletin of the Bureau of Fisheries, Vol. 

 XXX., 1910 (issued 1912). 



i Awnals of the Carnegie Museum, Vol. VIII., 

 No. 2, 1912. 



method of artificially infecting the common 

 and readily obtainable game fish, met with 

 little success. In 1912 I undertook the inves- 

 tigation of this problem. The previous nega- 

 tive results seemed to indicate that suitable 

 fishes were not being used. It seemed probable 

 that the parasitic glochidia, like other para- 

 sites, might be considerably restricted as to the 

 species of host to which they were adapted. 

 Working upon this theory I examined con- 

 siderable numbers of fishes taken at large, with 

 a view to finding those species that were 

 carrying in nature the glochidia of Quadrula 

 mussels. These studies supplemented by 

 experimentation in artificial infection con- 

 firmed the chief postulate of the theory, 

 namely, that there does exist a decided restric- 

 tion as to species of hosts for the glochidia 

 of some mussels. In the case of the warty- 

 back mussel, Quadrula pustulosa (Lea), for 

 example, I found infection restricted almost 

 exclusively to the Channel catfish, Ictalurus 

 punctatus (Eafinesque).^ The investigation 

 of these natural infections which has been 

 taken up quite extensively by Mr. T. Surber" 

 in the mussel investigations by the U. S. 

 Bureau of Fisheries, revealed other points of 

 interest. Among these was noteworthy the 

 entire absence of evidence of infection by some 

 common; species. Such observations for a 

 given species of mussel obviously indicate 

 something unusual in the life history. One 

 of the mussels for which I found no natural 

 infection and for which none have been re- 

 ported was Anodenta imhecillis (Say). 



During the first part of last November I 

 succeeded in securing several specimens of 

 this mussel. These were all gravid, as is usu- 

 ally to be expected, since this species is herma- 

 phroditic. Upon examining the contents of 

 the marsupium of one individual I found that 

 what at first glance I had supposed were 

 mature glochidia were instead juvenile mussels 

 with organs developed to the stage usually 

 seen at the end of parasitism when the young 



5 Howard, A. D., Transactions American Fish- 

 eries Society, 1912, pp. 65-70. 



6 ' ' Notes on the Natural Hosts of Freshwater 

 Mussels," Bull. Bureau of Fisheries, Vol. 22, 1912 

 (issued June 28, 1918). 



