EODO 169 



It seems to have a special predilection for long-standing infu- 

 sions of cod's head. It is a minute organism, only measuring 

 ■008 mm. in its longest diameter, and has the shape repre- 

 sented in fig. 36, A. The body is ovoid, somewhat compressed, 

 and drawn at one extremity into a point. This pointed 

 extremity is always directed forward in swimming. Immedi- 

 ately beneath it, rather to one side of the middle line, is a pit- 

 like depression continued along the flattened side of the body 

 into an oblique furrow. Instead of having a single flagellum 

 like Euglena, Bodo has two, both arising from the bottom of 

 the depression at the anterior end of the body. One of them, 

 always the shorter, is directed forwards, and is the active agent 

 in the free swimming movements of the animal. The second 

 flagellum, some two or three times longer than its fellow, is 

 known as the trailing flagellum, because during active 

 swimming movements it lies partly in the oblique furrow 

 which traverses the flattened side of the body and partly trails 

 out behind like a rope. The flattened side is usually called 

 the ventral, the opposite side the dorsal, but, as the former is 

 always directed upwards towards the observer during swimming 

 movements, the terms are not very well chosen. When 

 swimming, Bodo saltans does not progress in any definite 

 direction, but simply zigzags about in an apparently aimless 

 manner. 



The body consists of colourless protoplasm containing a 

 few granules and foreign substances which have been ingested 

 as food. Towards the middle of the body there is a vesicular 

 nucleus, and at the anterior end, close beneath the insertions 

 of the flagella, there is a contractile vacuole. A minute open- 

 ing, having the appearance of a vacuole, lying between the 

 bases of the flagella, is the mouth. It appears that this opening 

 is sometimes closed by co.nfluence of its walls, so that it must 

 be regarded as a temporary structure. From time to time 

 Bodo saltans ceases to swim about, anchors itself by its trailing 

 flagellum to some particle floating in the water, and then 

 executes a series of movements from which it has gained the 

 name of the springing Monad. The trailing flagellum is 

 spirally coiled, and then suddenly straightened out, and as 

 quickly coiled into a spiral again, so that the animalcule bobs 

 up and down in the water in a peculiar and very charac- 

 teristic manner. During these movements the anterior 



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