1918.] Baini Prashad : Glochidhun of Physnnio. 185 



tinuous structure all along the margin. It shows very fine ridges on its 

 ventral surface. Amongst the hookless glochidia like the present example 

 this flange must serve the same purpose as the tooth in the hooked 

 glochidia though perhaps in a less efficient manner. Between the two 

 valves of the shells a ligament is present and can be easily distinguished 

 in sections and stained preparations. 



The inside of the shell valves is lined by the larval mantle (figs. 

 6 and 7), which is formed of large cells. The cells have a conspicuous 

 nucleus and the cytoplasm is filled with a large number of minute granules. 

 In the mantle flap of each side two pairs of sensory cells (s.c.) can be 

 distingviished, one lying below the other. The adductor muscle (a. m. 

 figs. 9 and 6), which is seen as a whitish nearly circular area through the 

 shell in lateral view, lies near the anterior and dorsal margins of the shell. 

 The muscle consists of muscle-fibres stretching from one valve to the 

 other ; these fibres have elongated unclei and are seen to divide before 

 becoming attached to the valves. Lying just posterior and at a little 

 higher level than the adductor muscle is a triangular area ( an. figs. 3 

 and 7). This is the rudiment of the various organs of the future adult 

 mollusc. It consists of closely packed cells and extends a little below 

 the posterior margin of the adductor muscle. 



Fish hosL — It is a well-known fact that after being shed from the 

 marsupium, the glochidia, whether of the hooked or hookless type, 

 become attached to the gills or the fins of fishes and that each species 

 usually affects a single host or a group of closely allied hosts. 



The glochidia in the present case were seen attached to the caudal 

 fins of three species of fishes. The specific characters of the larvae can 

 be easily distinguished and hence the infection of the fish appears to have 

 occurred recently. The specimens were obtained at the end of February 

 and the beginning of March. The glochidia of P. micorpteroides were 

 found on the caudal fins of NemacMlus hrunneanus (fig. 8) and NemachilKs 

 brevis (fig. 9) ; both these species of fish were taken in streams. A single 

 glochidium of P. ferrvgineus was found, on the other hand, deeply em- 

 bedded in the caudal fin of Barilius auropurpweus (fig. 11). The two 

 species of Nemaclilus are found among weeds near or at the bottom and 

 the Barilius, though it usually swims near the surface, goes down to 

 the bottom at mid-day and was observed searching for insect larvae, etc., 

 in the mud at places at which P. ferrugineiis was abundant. 



LITERATURE. 



1. Lefevre, G., anp Curtis, W. C. — "Studies on the Reproduction 



and propagation of fresh- water mussels." Bulletin of 

 the Bureau of Fisheries, Washington, Vol. XXX, 1912. 



2. LiLLiE, F. R. — " The Embryology of Unionidae." Journal of Mor- 



phology, Vol. X, 1895. 



3. Ortmann. a. E. — " A monograph of the Najades of Pennsylvania." 



Memoirs of the Cnrneiiie Museum, Pittsburgh, Vol. IV, 

 1911. 



4. Simpson, C. T. — " Synopsis of the Naiades or pearly fresh-water 



Mussels." Proceedinqs of the Vniled States National 

 Museum, Vol. XXII, 1900. 



