470 



Dr. Wallich on the RMzopods. 



faces, the entire intervals being 

 studded witli much more minute 

 disks or globules (for it is almost 

 impossible to determine positively 

 which they are). We have in this 

 and also in fig. 5 typical exam- 

 ples of the pyriform test of 

 Difflugia jpyrvformis^ the only 

 diiference between them consist- 

 ing in the degree of inflation in 

 the body, of the test — a differ- 

 ence which is shown to extend 

 still further in pis. xxii. and xxiii. 

 of ^^Nebela collaris '^ in Prof. 

 Leidy's work. In fig. 5 (a 

 Greenland form) very minute 

 specimens of a diatom, probably an Eunotia, take the place of 

 some of the colloid disks. It is, 

 however, in the series of tests which 

 are chiefly built up of diatoms that 

 a clue is found to the formation 

 of the large and small colloid 

 disks, and rectangular siliceous 

 plates derived from this source. 

 In some tests the process of meta- 

 morphism can be very distinctly 

 traced, and we then see in differ- 

 ent specimens and different 

 varieties a gradual passage from 

 their original figure to one or 

 other of the various metamorphic 

 forms of which mention has been 

 made. Where large oval or cir- 

 cular diatom-valves have formed 



part of the test these appear, in some of Prof. Leidy's figures, 

 to pass eventually into true circular or oval hyaline plates of 

 proportionately large dimensions. 



1 have only space to add that the appearances described as 

 characterizing the metamorphic series are not confined to the 

 mitriform and pyriform varieties, though they would appear to 

 reach their climax in them. They are likewise observable 

 in the globular and oblique, or, as 1 have termed it, the mar- 

 supiiform series, of which Difflugia spiralis and D. cassis 

 are offshoots. In the former of these two the chitinous pellets 

 and cylinders, whether straight or bent, seem to arrive at their 

 maximum of development. But, strange to say, I have never 



