1 66 



MORPHOLOGY. 



Class Peridineae. 



358.7. These are peculiar one-celled organisms pro^■idccl with two flagella 

 and show some relationship to the Flagellates. They usually are provided 

 with a cellulose memhrane, which in some ffjrins consists of curiousl}' 

 sculptured plates. In the higher forms this cellulose memfirane consists of 

 two valves fitting together in such a way as to resemble .some of the diatoms. 

 Like the Flagellates, some ha^"c green chromatophores, ^\"hich in some are 

 obscured by a yellow or brown pigment (resemlihng the diatoms), while 

 still others have no chlorophyll. The Peridineie are abundant in the sea, 

 while some are found in fresh water. 



Class Diatomaphyceae ( Bacillariales, Diatomaceee). 



3586. The diatoms are minute and peculiar organisms believed to be 

 algje. They live in fresh, brackish, and salt water. I'hey are often found 

 covering the surface of rocks, stii ks, or the scjil in thin .sheets. They occur 

 singlv and free, or se^■eral indiN'iduals ma\' V)e joined into long threads, or 

 other species may be attached to objects by slender gelatinous stalks. Each 

 a It c d i '. 



Fig. lyra. 

 A grr.np nf Di:it'irns: c and d, tup and side views of the same form; p, colony 

 of stalked Innris attached to an alga: f and ^', top and side views itf thr fnrm sliown 

 at e; /i, a ci tli"in\'; i, a cijlnny, the ti>i' and siilc \ic\v shi.i wn at k and i;, fi Tming aux< i- 

 spores. (.\ftcr Jvfrntr.) 



protopla.st is enclosed in a silicified skeleton in the form of a box with two 

 halves, often shaped like an old-fashioned |iill box, one half titling o\er the 

 other like the lid of a bo.x. It is e\ideiU that in this condition the plant 

 cannot ini rease much in size. 



They multiply by fission. 'I'his takes place longitudinally, i.e., in the 

 direction of the two halves or vnjvcs of the box. I\ach new ytlant then has a 

 vah-e onh' on cme side. .\ new \alve is now formed o\er the naked half, 

 and fits inside the old \Td\'e. .\[ each <li\ision the indi\iduals tluis becc")me 

 smaller and smaller until {\\i\ rea(~h a ( erlain point, when the \al\-es arc 

 cast off and the cell f<irncs an nn\i>s j^in'r, i.e., it grows alone, or after conju- 

 gation with anolhir, to the full si/e again, and e\'entually provides itself 



