June 2, 1911] 



SCIENCE 



865 



tion this was found to be true, and it was dis- 

 covered that these young mussels — for such 

 they undoubtedly are — are subsequently lib- 

 erated by the disintegration of the cord after 

 having passed through the metamorphosis in 

 the entire absence of a parasitic period. We, 

 therefore, have concluded that the emergence 

 from the cords in the glochidial stage is pre- 

 mature — 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 have 

 reached as advanced a stage of development as 

 is attained by any unionid at the time it leaves 

 the fish. They closely resemble the young of 

 Anodonta at the close of the parasitic period, 

 and upon examination have been found to 

 possess the following structures: the anterior 

 and posterior adductor muscles; the ciliated 

 foot ; two gill buds on each side ; a completely 

 differentiated digestive tract, including mouth, 

 oesophagus, stomach, intestine and anus ; liver ; 

 the cerebral, pedal and visceral ganglia; oto- 

 cysts ; the rudiments of the kidneys, heart and 

 pericardium; and also a slight growth of the 

 permanent shell around the margin of the 

 shell of the glochidium. The larval muscle 

 has completely disappeared, although some of 

 the mantle-cells of the glochidium, as well as 

 the hooks of the shell, are still present. They 

 crawl slowly on the bottom of the dish by the 

 characteristic jerking movements of the foot, 

 after the manner of the young of other species 

 at a corresponding stage, although the valves 

 of the shell gape more widely apart and the 

 foot is shorter and less extensible. We have 

 not succeeded as yet in keeping; them alive for 

 more than ten days, but it is difficult in the 

 case of any species to maintain young mussels 

 of this age under laboratory conditions. 



Since these young mussels do not re.spond to 

 the stimuli which cause glochidia to close the 

 shell and all attempts to bring about their 

 attachment to fish have failed, and, further- 

 more, since their behavior in creeping on the 

 bottom is characteristic of post-parasitic life, 

 it would seem clear that no subsequent para- 

 sitism is possible. The conclusion is, there- 

 fore, inevitable that we have here to do with a 

 species which has no parasitism in its life- 

 history, although the presence of hooks and 

 other typical glochidial structures would indi- 

 cate that it has originated from ancestors 

 which possessed the parasitic stage like other 

 fresh-water mussels. The cord is undoubtedly 

 to be interpreted as a nutritive adaptation 

 which arises in the marsupium during the 

 early stages of gravidity, since the young em- 

 bryos are at first contained in an unformed 

 viscid matrix and the cords are a later product. 



The whole history of this exceptional 

 species warrants a more detailed study, and 

 Miss Young is now engaged in such an in- 

 vestigation. When her work is completed, we 

 hope that it may include the entire course of 

 development, the method of formation of the 

 cords, and the rearing of the young mussels 

 during a much longer period than has thus far 

 been possible. 



George Lefevee, 

 WiNTERTON C. Curtis 



University of Missouri, 

 March 25, 1911 



THE SCALES OF THE ALBULID FISHES 



Albula.has long been regarded with unusual 

 interest by ichthyologists, being an isolated 

 type standing near the base of the Teleostean 

 series. It is exceptional among all teleosteans, 

 Boulenger remarks, in having two transverse 

 series of valves to the bulbus arteriosus in- 

 stead of one; an approach to the condition of 

 the " Ganoids," in which there are three. Gill 

 admits the " Ganoids " into the teleostean 

 series, and according to his arrangement 

 Amia falls in the order Cycloganoidei, just 

 before or below the Malacopterygii, of which 

 Albula is a primitive member. In Smith- 

 sonian Misc. Coll., Vol. 56, No. 3, p. 2, I have 



