REPRODUCTION AND ARTIFICIAL PROPAGATION OF FRESH-WATER MUSSELS. 1 73 



discharge of the cords by the female; but we removed them from the marsupium, placed 

 them in water, and, after the glochidia had emerged (fig. 46, pi. xii), employed various 

 means to bring about their attachment to fish. None of these attempts, however, was 

 successful, although the fish were left in small dishes containing many cords for as long 

 a time as 1 2 hours. In the light of these results, which indicated the inabilit}' of this 

 glochidium to attach itself to fish, and in view of the fact that the cords so evidently 

 seemed to be a nutritive device, we felt it to be highly probable that in this species the 

 metamorphosis would be found to occur in the absence of parasitism — a prediction 

 which has been recently verified. 



On February 6, 191 1, a single female of Strophitus edeniuhis, which had been kept 

 in the laboratory since the preceding November, was seen discharging its cords from 

 the exhalent siphon. The discharge continued until March 25, and during that time 

 the cords were thrown out in varying numbers from day to day. They measured from 

 2 to 10 mm. in length and about i mm. in diameter, although they became more or 

 less swollen after lying in the water for a time. Each cord contained from 10 to 24 

 glochidia arranged in an irregular row. In many cases the glochidia emerged from the 

 cords in a few minutes after the latter were discharged, and then usually remained 

 attached by the thread in essentially the same manner as has been described by Lea 

 and Sterki (fig. 46, pi. xii). The thread, which is apparently a modified lar\-al thread, 

 is continuous at its distal end with the egg membrane, w'hich generally remains embedded 

 in the cord; so intimate, in fact, is the union between the two that at times the mem- 

 brane, adhering to the thread, is dragged out of the cord when the glochidium is 

 extruded, in which case, of course, the glochidium becomes entirely detached from the 

 cord. 



All attempts to infect fish with these fully formed glochidia were again unsuccessful, 

 even when the exposure was of long duration. Within a few days the extruded glochidia 

 died in spite of every effort to provide the most favorable conditions for their maintenance. 



When the cords first began to be discharged, one of our students, Miss Daisy Young, 

 happened to notice that not all of the larvae were extruded, and that among those which 

 remained in the cords some had lost the larval adductor muscle, possessed a protrusible 

 foot, and showed other signs of having undergone the metamorphosis. Upon careful 

 examination this was found to be true, and it was discovered that these young mussels — 

 for such they undoubtedly are — are subsequently liberated by the disintegration of the 

 cord after having passed throtigh the metamorphosis in the entire absence of a parasitic 

 period. We, therefore, have concluded that the emergence from the cords in the glo- 

 chidial stage is premature, due possibly to some change which has taken place in the 

 gelatinous substance surrounding them as a result of free contact with the water, or to 

 release from the pressure to which they are subjected while in the marsupium. It is 

 perfectly evident that these glochidia neither become attached to fish nor undergo any 

 further development; they have simply come out too soon and are lost. 



The young mussels, on the other hand, which have developed inside the cords, when 



liberated by the disintegration of the latter or removed directly by teasing, are found to 



85079°-BuU. 3c 



