GLOCHIDIUM OF ANODONTA 



147 



order to secure this attaclinieiit, the lar-s'a, wliich is generally 

 Iciiowu as Glochidium, develops a long flLinient which perhaps 

 renders it aware of the neiglibourhood of a fisli, and also a. 

 larval shell furnished with strong hooks l)y which it fastens 

 itself to the body of its unconscious host (Fig. 56). According 

 to some interesting observations made l)y Mr. O. H. Latter,' 

 the ova pass into the external gill of the motlier, in which is 

 secreted a nutritive mucus on which they are sustained until they 

 arrive at maturity and a suitable opportunity occurs for their 

 ' being born.' If this opportunity is deferred, and the Glochidia 

 mature, their so-called ' byssus ' becomes developed, and ])y Ijeing 



o.ad 



A 



B 



Fig. 56. — A. Glocliidium immediately .ifter it is liatclied : ad, adductor muscle; by, 

 ' by.ssus ' cord ; s, sense organs ; sit, shell. B. Glochidium after it lias been on tlie 

 lisli for some weeks : a.ad, p.ad, anterior and posterior adductors ; al, alimentary 

 canal ; ai(.v, auditory vesicle ; hr, branchiae ; /, foot ; mt, mantle. (Balfour.) 



entangled in the gill filaments of the parent, prevents their 

 escaping. It is interesting to notice that, when the nutritive 

 mucus of tlie parent is used up, it becomes, as it were, the 

 turn of the children to provide for themselves a secondary mode 

 < )!' attachment. 



The mother Anofh)nt(( does not always retain the Glocliidium 

 until fish are in her neiglibourhood. Cientle stirring of the 

 water caused them to emit Glochidivni, in large masses, if the 

 movement was not so violent as to cause alarm. The long slimy 

 masses of GlochidiuriL were observed to be drawn back again within 

 the shell of the mother, even after they had been ejected to a 

 distance of 2 or 3 inches. 



It is a mistake to assert that the young GlocJiidiuvi can swim. 

 AVhen they finally quit the nK)ther, they sink to the bottom, 



^ P. Z. S. 1S91, p. r>2 f. 



