560 



THE AMERICAN MUSEUM JOURNAL 



The glochidium is a stage at which de- 

 velopment ceases and death ensues un- 

 less the larva becomes attached as a 

 parasite upon a fish.~ The gaining of 

 this favorable environment within the 

 fish's tissues is wholly accidental; and 

 so many glochidia perish that they 

 must be produced in enormous numbers 

 in order that the chances of destruction 

 be overcome and the continuance of the 

 species assured. 



When we examine the paths followed 

 in the establishment of the facts above 

 outlined, it happens that the trail 

 again begins with Leeuwenhoek. Be- 

 fore his day it was not even known 

 whether there existed in these lowly 

 organisms anything comparable with 

 the "maleness" and "femaleness" rec- 

 ognized in higher forms. Their whole 

 mode of generation, whether spon- 

 taneous or by means of eggs, was a 

 matter of dispute. In his efforts to 

 solve these fundamental, but at the 

 time wholly academic questions, Leeu- 

 wenhoek turned his microscope upon 

 the fresh-water mussels and discovered 

 the innumerable eggs and larvae which 

 crowd the brood-pouches. These he 

 correctly interpreted as the young of 

 the mussel in which they were found ; 



and it is clear from his descriptions 

 tliat he saw enough of their develop- 

 ment to justify his opinion that mus- 

 sels, like the more familiar forms of 

 animal life, arose from eggs. In the 

 sulisequent advance of our knowledge 

 two periods are conspicuous, one marked 

 by a mistaken hypothesis, the other by 

 the discovery of the parasitism. The 

 first period, which extends from 1797 

 to about 1830, was ushered in when 

 the failure to secure stages beyond 

 the glochidium led to the so-called 

 "Glochidium Theory," which main- 

 tained that the larvae were not the 

 young of the mussel in which they were 

 found l)ut a wholly different species liv- 

 ing within the mussel as a parasite. 

 This theory had the one advantage of 

 all incorrect hypotheses; it aroused op- 

 position which in turn called forth in- 

 vestigations. These showed once for 

 all that the glochidium was the young 

 of the mussel in whose l^rood-pouch it 

 was found. 1 



Disproof of the glochidium theory 

 left the facts regarding the subsequent 



^ In passing, it is of interest that the word 

 "glochidium," by which we still designate these 

 larvae, had its origin at the period when the sup- 

 posed parasites were described as a species which 

 parasitized the mussel and were named Glochidium 

 parasiticum. 



Coxi.rtesy of the United States Bureau of Fisheries 

 Seining fish in Lake Pepin, Minnesota, for mussel propagation, and transferring the fish to the in- 

 fection tank. — The supply of fish for this purpose is obtained chiefly by seining in the public waters. 

 Overflow ponds near the course of rivers which under natural conditions dry up leaving the fish to 

 die, are seined out, and those species suitable for infection with mussels are used in that work. After- 

 ward, these, together with the other fish taken, are liberated in the river, thus reclaiming large num- 

 bers of fish which otherwise would be lost — as well as propagating the mussels 



