Aquatic Mtt 



112 



native waters. These three shells all 

 measured about n cm. in greatest length. 

 The writer strongly recommends these to 

 aquarists as at no time have they been 

 known to indulge in "plowing" up the 

 bottom of the aquarium, being content to 

 remain in practically any position. They 

 have been only rarely noted to shift 

 their position and then usually not more 

 than half the length of the shell. At no 

 time have they been in aquaria containing 

 sand in sufficient quantity to completely 

 cover their shells. No particular care 

 has been bestowed upon them at all, 

 simply being placed in the aquarium and 

 forgotten. The amount of food that they 

 have been able to draw from the sus- 

 pended material in the crystal clear water 

 of the aquarium has evidently been suf- 

 ficient to maintain life. It is generally 

 believed that their presence aids in keep- 

 ing the water in such a condition, al- 

 though they are apparently by no means 

 essential. 



Shortly after arriving at Washington, 

 several individuals of other species emit- 

 ted glochidia, the larval form in which 

 these organisms start their life. These 

 are little bivalved creatures that normally 

 have the valves widely spread, but on 

 slight stimulation of the ligament con- 

 necting the two, they are brought to- 

 gether with considerable vigor. In this 

 manner they are able to attach them- 

 selves to fish, different species of mussels 

 requiring different hosts for their pur- 

 pose, which is one of parasitism. This 

 attachment occurs usually on the gill fila- 

 ments or on the fins. In a short time 

 the injured tissue grows over and around 

 the animal, completely encysting it. En- 

 closed in this cyst the young mussel 

 further develops and finally breaks out 

 of it to lead its sedentary existence on 

 the river bottom, apparently leaving the 

 fish none the worse for its experience. 



Il is evident (hat as well as protecting 

 and nourishing the mussel in its early 

 and most precarious time of life the dis- 

 tribution of the species is niueh more ef- 

 fectively accomplished by this parasitic 

 habit, as the host may carry it much 

 farther than its sluggish adult movements 

 could ever hope to. 



Two periods are thus brought into the 

 life of every mussel when its existence 

 hangs by a very slender thread, depend- 

 ent solely on external circumstances; 

 first when it is emitted as glochidium, 

 here depending on the passing of a luck- 

 less fish of proper species, in the absence 

 of which it perishes in a short time ; and 

 second when it leaves the fish and faces 

 the possibility of falling onto an unsuit- 

 able bottom, such as one covered with 

 flocculent mud, which would smother it, 

 or into water too deep to allow its exist- 

 ence. It is almost needless to add that 

 for every one which survives, thousands 

 fail at either of these vital times. To 

 counteract this and insure the perpetua- 

 tion of the species countless numbers of 

 glochidia are discharged from the brood 

 chamber of the parent mussel, where they 

 have been incubated, to the time when 

 they are ready to take their chances in 

 the outside world. Aquarists need have 

 no fear of infecting their various fishes 

 as the possibility of any of the usual 

 aquarium fish being suitable hosts for 

 these species is very remote. 



Explanation of Plate 



i. Living glochidia of Lauipsilis liga- 

 ment ina, as seen through the microscope, 

 one hour after expulsion. Magnification. 

 40 diameters. 



2. Lauipsilis ligamentina. Length, 

 1 1.5 centimeters. 



3. Lauipsilis anodontiodes. Length. 10 

 centimeters. This species has the great- 

 est commercial value. The shell exter- 

 nally is a rather pleasing shade of yellow. 



4. Lauipsilis anodontiodes with syphon 

 extended. ( Photographs by the author.) 



