1921] NATURAL SCIENCES OF PHILADELPHIA. 145 



dorsal side, which at the anterior end is not infrequently drawn 

 out into a point. Anterior end diagonally truncated. . . ." In 

 spite of all descriptions, however, it would be very difficult to recog- 

 nize a Cryptomonas without a few explanatory figures, so much 

 the more, that the form of the body is exceedingly variable, from 

 that of an egg to that of a curved spindle. The size also varies 

 within very Avide limits, most of the specimens measure from 30 to 

 55[x in length, but some are very much smaller. At the end of 

 September, for instance, a multitude of very small individuals sud- 

 denly appeared, which though certainly belonging to this species, 

 measured only from 12 to 13[x (Plate VIII, fig. 56) , they were nearly 

 oval in form, but grew nearer and nearer the typical form, in the 

 same proportion as the size augmented. 



Let us now consider in its more intimate structure, such an indi- 

 vidual as is shown by Plate VIII, fig. 55, which represents fairly 

 well the typical Cryptomonas ovata. The organism is seen with 

 its ventral side to the right, the dorsal convex one to the left, 

 terminating in a point, or beak-like extremity, the posterior part of 

 the body is rounded, the anterior diagonally truncated, and hollowed 

 into a depression whose deepest part is nearer the ventral side. 



The most exterior part of the body is represented by a colorless 

 periplast, of a cellulose nature, in the substance of which extremely 

 fine granulations are dispersed, whose significance, as we shall later 

 see, is that of trichocysts. Inside the colorless investing layer are 

 the chromatophores, olive-green as a rule, in the form of two curved 

 laminae which are applied to nearly the whole inner face of the 

 external layer, and joining each other by their respective borders 

 with such precision that one might think of one chromatophore 

 instead of two. They are, however, not very distinct, except on 

 their right and left sides, on account of their being seen there through 

 a greater thickness. The green laminae are paralleled on their 

 internal face by a continuous sheet of grains of starch, sometimes 

 so much pressed against each other as to deform into hexagona 

 facets, but always making only a single layer. These starch grains 

 must be regarded as a direct product of the chromatophores, and 

 at the same time as a food-reserve, for they disappear in twenty- 

 four hours with unfavorable conditions of life. Besides these amy- 

 laceous grains, others of quite another nature are found ; large shining 

 bodies, very generally two in number (sometimes one and rarely three) 

 showing indistinct crystalline forms which might apparently be 

 referred to the hexagonal system; they are always found in the 

 same position, not far from the dorsal side, and just dorsal to the 

 characteristic "cage" that will be spoken of later. These special 

 bodies, which might be compared to the oxalate crystals of Rhizo- 

 pods and Infusoria, are nearly always present, an interesting fact 



