REPRODUCTION AND ARTIFICIAL PROPAGATION OF FRESH-WATER MUSSELS. 1 37 



usual condition, the conglutinates are similarly modified. In Obliqiiaria reflexa, for 

 example, in which the marsupium consists of several elongated and distended water tubes 

 of tubular form, the conglutinates are large, slightly curved cylindrical masses of nearly 

 uniform diameter and generally blunt at each end. Three of them are shown in figure 

 42, plate XI; the one on the right was taken from the most posterior water tube of the 

 marsupium, which is not as long as the rest, and its conglutinate is correspondingly 

 shorter. The relation will be understood by reference to the figure of the marsupium 

 of this species (fig. 7, pi. vii). 



There seem to be two methods by which the embryos are bound together to form 

 conglutinates — they may either be attached more or less firmly to each other by their egg 

 membranes, which are in this case of an adhesive nature, or they may be embedded in a 

 mucilaginous matrix of varying consistency. The former is by far the commoner condi- 

 tion and is seen in figure 17, plate viii, which is a detail drawn from one of the congluti- 

 nates of Obliquaria reflexa shown in figure 42, plate xi; the immature glochidia with their 

 valves open are still contained within the membranes, which are closely adhering and by 

 mutual pressure are squeezed into a polyhedral form. In cases like this it is difficult to 

 determine whether there is a glutinous matrix between the embryos or not, but if any is 

 present, it must be in very small amount, since the embryos seem to be held together 

 solely by the adhesive surfaces of their membranes. In those cases, however, in which a 

 matrix is evident {Lanipsilis), the embryos are not so closely appressed and are embedded, 

 more or less loosely, in a glutinous binding substance. This condition is illustrated in 

 figure 16, plate viii, which is a portion of a conglutinate of Lanipsilis liqamentina seen 

 under higher magnification; as the matrix is transparent, it can not be shown in the 

 figure. 



The conglutinates differ markedly in tenacity, for, whereas in some cases the mutual 

 adhesion is not strong and the masses consequently break up readily {Quadrula , Pleu- 

 robema, Unio, Lampsilis), in others (notably in Obliquaria) the embryos adhere so firmly 

 that they may be separated only with difficulty by teasing. 



In still other species the embryos can not be said to form conglutinates at all, as 

 they are merely suspended in a slimy mucus which is not of such a consistency as to 

 enable the mass to maintain a definite form when removed from the gill. We have 

 observed this condition in Alasmidonta, Anodonki, and Symphynola, and Ortmann (191 1) 

 states that it also occurs in Anodontoides . 



In most species {Quadrula, Unio, Lampsilis, Dronius) in which the conglutinates 

 are found, the adhesion exists only during the embryonic development and by the 

 time the glochidia are fully formed they are found to be free but for the mucus which 

 holds them more or less loosely together. In Obliquaria reflexa, however, the congluti- 

 nation persists, and the fully developed glochidia, still tenaciously adhering, are dis- 

 charged from the marsupium in the cylindrical masses already described (fig. 42, pi. xi) ; 

 even after lying in the water for some time they do not separate, and it has perplexed 

 us to understand how the glochidia of this species ultimately become attached to fish, 

 if they pass through a subsequent parasitic stage. Can it be that parasitism has been 



