OMNIVOROUS ECHINODERMS, &c. 



!7J 



to the water. It has no popular name, but to avoid using the 

 somewhat long-winded scientific one {Hcematococais pluvialis) 

 (fig- 473). we may perhaps call it the Berry Animalcule. It is 

 to be found both in a "resting" and a "motile" stage. In the 

 former condition it appears as a minute sphere, either entirely 

 green, or more or less red from the presence of a second pigment 

 in addition to the chlorophyll. The sphere owes its definite form 

 to the presence of a delicate bounding membrane (cell-wall) com- 

 posed of a substance (cellulose) characteristic of plants, though not 

 entirely limited to them. Cellu- 

 lose is closely related to starch, 

 and ordinary cotton is a very 

 pure form of it. There is no 

 trace of mouth or digestive cavity, 

 and the food consists merely of 

 carbonic acid gas, water, and 

 simple mineral salts, and if our 

 knowledge of the Berry Animal- 

 cule were limited to this resting- 

 stage we should undoubtedly look 

 upon it as a low green plant. 



But we also find it in a "motile" condition, when it is capable 

 of executing active swimming movements. Under these circum- 

 stances the living substance of the body is pear-shaped, with a 

 couple of whip-like flagella projecting from the clear narrow end, 

 and effecting active locomotion by means of their lashing move- 

 ments. In this case the cell-wall may either be entirely absent 

 or it may be seen investing the body some little distance from the 

 pear-shaped body-mass, and pierced by the projecting flagella. 

 As before, no special digestive organs are present, while the 

 food and way of feeding are entirely plant-like. Considered by 

 itself, we should be justified in considering the Berry Animalcule 

 as a plant, and its powers of active movement in one stage of the 

 life-history is no particular bar, for many lower green plants (algae) 

 about whose nature there is no question propagate by means of 

 minute actively -moving "zoospores" of fairly similar character. 

 Most botanists accordingly claim this organism as a plant, and 

 it will be found described as such in standard text-books of 

 botany. Many zoologists, however, look upon the Berry Ani- 

 malcule as an animal which feeds like a plant, basing their 



Fig. 473. — Berry Animalcule [Hiematococctts plwui' 

 alls), greatly enlarged, a, Resting stage; B, motile 

 stage: c.w. cell-wall; n. nucleus;^, flagella. 



Vol. II. 



50 



