GENUS DIFFLUGIA— DIFFLUGIA PYEIFOEMIS. 103 



formis consists of chitinoid membrane, colorless or straw-colored, and 

 having incorporated variable quantities of diatoms and sand, as seen in figs. 

 22-26, pi. X. Specimens of this kind, of the smallest size, occasionally 

 met with, are remarkable for the great proportionate size of the adherent 

 diatoms, as seen in figs. 22, 23, reminding one of the cases of the basket- 

 worm (Thyridopteryx), often seen suspended from the branches of the arbor- 

 vitse and other trees. 



Rarely I have seen a Difflugia, referable to D. pyriformis, in which 

 the shell appeared to be composed of chitinoid membrane incorporated 

 with flocculent black matter, apparently from the sediment of the locality 

 in which the creature was found. Such a specimen is represented in fig. 

 27, pi. X. 



The shell of D. pyriformis, in all the specimens included as varieties 

 under the names of D. compressa, D. nodosa, D. vas, and D. comuta, as seen 

 in the various figures of these, in plates XI and XII, was composed exclu- 

 sively of angular particles of quartz-sand. Rare, indeed, is it to see a 

 rounded particle of quartz-sand entering into the construction of the shell 

 of any Difflugia ; but an example of one such shell, pertaining to D. pyri- 

 formis, exhibiting several rounded sand grains, is seen in fig. 15, pi. X. 



The interior sarcode of Difflugia pyriformis, as usual in the genus from 

 the nature of the shell, is greatly obscured from view. Commonly, the 

 greater portion of the mass occupying the body of the shell is of a bright 

 green color due to the presence of an abundance of chlorophyl granules, 

 which appear to be an intrinsic element of structure of the endosarc. 

 Less frequently the sarcode appears to be in greater part or even entirely 

 colorless, except that the central portion may be more or less colored 

 by the presence of food contents. 



The expressed sarcode of I). pyriformis usually exhibits a faintly 

 granular and colorless basis mingled with variable propoi-tions of bright 

 green chlorophyl granules, and others which are colorless and darkly defined 

 and resemble starch. Besides these, there may be seen a large and clear or 

 faintly granular nucleus, together with the varied constituents of the food. 

 In individuals with uncolored sarcode, the chlorophyl granules are absent, 

 and such also appears to be the case with most of the starch-like granules. 

 Sometimes, in the bright green specimens, the expressed nucleus exhibits a 

 uniform and distinct granular appearance. Mr. Carter, in an account 



