466 Dr. Wallicli on the Rhizopods. 



observations on this organism in the year 1848 show he 

 was aware of Ehrenberg having discovered and drawn atten- 

 tion to the form in question {vide Leidy, p. 150). But it also 

 adds another powerful reason to those I have abeady adduced 

 why the transition forms referred by me to Diffiugia should be 

 retained in this genus*. It will be seen that Ehrenberg 

 described the test as '■'■ pyriform.^'' 



After having stated ('Annals,' May 1864) that no vegetable 

 or extrinsically derived substances are, in my experience, 

 employed for the consolidation of the Difflugian tests, I 

 alluded to the selective faculty of the animals as being so 

 remarkabie that colourless mineral particles, sometimes quart- 

 zose, sometimes felspathic, sometimes micaceous, seem to be 

 always chosen, as one or other of those minerals happens to be 

 present in the mud of the locality inhabited by them, and that 

 the particles are impacted into the chitinoid matrix in so 

 workmanlike a manner as to leave only the smallest intervals 

 between adjoining masses and as little overlapping as possible. 

 Keference was next made to the fact that the testaceous forms 

 when living in streamlets, where they incur a risk of being 

 swept away, reduce this risk to a minimum by loading their 

 tests with as large particles of mineral matter as they can 

 utilize. It was also stated that the mineral particles used 

 are not always of inorganic origin, diatoms of various kinds 

 being promiscuously employed in some tests, whereas in 

 others a selection has been made of one kind only out of the 

 various forms present in the same habitat. And, finally, I re- 

 marked on the metamorphic forms of Difflugidas, belonging for 

 the most part to the mitriform and pyriform series, in which 

 the chitinoid matrix of the tests presents no appreciable 

 admixture with unmetamorphosed mineral matter, but is more 

 or less closely covered over with composite bodies of various 

 forms and sizes. Tlie whole of the forms now referred to were 

 minutely described as they present themselves to us in the 

 metamorphic series, of which figures are given in the plate 

 attached to my paper above referred to. 



My reasons were then expressed for arriving at the con- 

 clusion that, except in the case of a few permanent varieties 

 which present a type capable of being hereditarily trans- 

 mitted, the whole of the varieties of Difflugian tests may be 

 regarded as the result, first, of modifications in figure, 

 dependent sometimes on the inability of the test to sustain its 



* Ehrenberg's definition of D. collaris is as follows : — " D. coUai-is, 

 n. sp. -D. lorica sub ostio in colli formani attenuata, pyrifomii, subcla- 

 vata recta, superficie irregulariter ce//if/osa (!), cellulis parvis fequalibus, 

 colli angustioribus, apertura Integra" (Monatsb. 1848, p. 218). 



