GLOCHIDlUiM OF ANODONTA 



147 



parasitically attached to certain species of fresh-water fishes. In 

 order to secure this attachment, the larva, which is generally 

 known as G-lochidium^ develops a long filament which perhaps 

 renders it aware of the neighbourhood of a fish, and also a larval 

 shell furnished with strong hooks by which it fastens itself to 

 the body of its unconscious host (Fig. b^'). According to some 

 interesting observations made by Mr. O. H. Latter,^ the ova 

 pass into the external gill of the mother, 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 Grlochidia 

 mature, their so-called 'byssus' becomes developed, and by being 



Fig. 56. — A, Glochiduim immediately after it is hatched: ad, adductor muscle; by, 

 'byssus' cord; s, sense organs; sh, shell. B, Glochidlum after it has been on the 

 fish for some weeks: a. ad, p. ad, anterior and posterior adductors ; aL alimentary 

 canal; au.v, auditory vesicle; br, 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 the parent is used up, it becomes, as it were, the turn 

 of the children to provide for themselves a secondary mode of 

 attachment. 



The mother Anodonta does not always retain the Gloehidium 

 until fish are in her neighbourhood. Gentle stirring of the 

 water caused them to emit G-lochidium in large masses, if the 

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

 slimy masses of Glochidium 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 Glochidium can 

 swim. When they finally quit the mother, they sink to the 



1 P. Z. S. 1891, p. 52 f. 



