38 



LOWER INVERTEBRATES. 



Fig. 33. — Cilio-flagellate, en- 

 cysted, enlarged 300 times. 



but recent investigations have considerably enlarged its borders. It now embraces five 

 families, the typical forms being included in the Peeidinid^. These are free-swim- 

 ming animalcules, sometimes naked, but in most cases the body is enclosed in a hard 

 case, variously ornamented, the angles sometimes being i^rolonged into long spines. 

 The case or cuirass has recently been proved to be cellulose, a substance hitherto only 

 known in the Ascidians, outside of the vegetable kingdom. The cilia occur as a central 

 or eccenti'ic girdle, more or less complete ; in the cuirassed forms the shell is usually 

 divided by a groove, the borders of which are ciliated. The shell is either composed 

 of one uniform piece or is made up of plates. There arise from some parts of the body 

 one or more flagella. In life these flagella are seen to suddenly disappear, and a close 

 examination has shown (in Ceratium) that there is a small cavity situated at the base 

 of the flagellum into which that organ retreats, bringing with it foreign bodies which 

 serve for food. The nucleus is usually spherical or oval, 

 while a contractile vacuole is occasionally found. They are, 

 like Nbctiluca, highly phosphorescent. They have been ob- 

 served to become encysted, when segmentation, on a more 

 or less extensive scale, occurs. In some cases the cyst is en- 

 closed in the carapax ; in other instances the cuirass is thrown 

 off, and a new cyst of a different form is secreted, which often 

 has one or both extremities prolonged into attenuate curved 

 homs, giving it a crescent shape (Fig. 33), resembling certain desmids ( Closteria). They 

 sometimes hibernate in this condition. They occur in both salt and fresh water. 



Of the ten genera of the Peridinidse the species of three are naked, that is, resemble 

 in essentials those of the loricate forms which have thrown off the 

 case previous to encystment. Gymnodinium pulvisculus is, per- 

 haps, as often met with as any; it occurs among Algae in pools, 

 often in great numbers, is somewhat spherical, with a transverse 

 groove, and is brown or yellow in color. The best-known genera 

 are Glenodinium, and Peridinium without horn-like processes, and 

 Ceratium., with conspicuous processes on the 

 shells. G. cinctum is well known to observers 

 of pond-life ; its smooth case should distinguish it 

 from a similar Pmc?mi?<m with faceted carapax. 

 These genera are represented by several species in American waters. 

 Mr. H. J. Carter has described a most remarkable instance of the 

 coloring red of the waters around the shores of the Island of Bom- 

 bay by P. sanguinea. During its active stages this species is green 

 and translucent ; gradually, as the time approaches for it to assume 

 its quiescent or encysted state, refractive oil globules appear within 

 the interior, and the green gives place to red, and thus the water 

 containing them acquires a deep vermilion hue. It is probable 

 that other instances of red waters are due to similar causes. The 

 characteristic Ceratium (Fig. 35) appears to be a cosmopolitan 

 infusorian. It has been known a long time as C. longicome, but 

 R. S. Berg has recently indentified it with JBursaria hirundindla 

 of O. F. Muller, which, if correct, will change the specific name to 

 the one having priority.- C. hirundinella occurs often in large 

 numbers in the water-supply of all the cities along the Great Lakes. It is most abun- 



PiG. 34. — Gymnodin- 

 ium lachmannii 

 dividing, greatly 

 enlarged. 



Fia. 35. — Ceratium hirun- 

 dinella, enlarged 300 

 times. 



