ZOOLOGY AND BOTANY. MICBOSCOPY, ETC. 
643 
cell, while an “ endocyte ” is any cell which forms part of a surface of 
the central cavity of a sponge, including the efferent system of canals 
and the flagellate chambers. Normally, the collar cells are short and 
barrel-shaped with separate cylindrical collars which are never united. 
In certain pathological conditions, probably connected with suffocation, 
they elongate very greatly, diminishing in the diameter of their upper 
part and in some species even coming into contact. “ Sollas’ mem- 
brane ” is always associated with great distortion of the cells. Where 
there is no distortion there is no membrane. The collar in Sycon 
compressum is made up of about 30 parallel rods united by a film of 
some other substance. The flagellum is intimately connected with the 
nuclear membrane. There is an interstitial substance between the body 
of the cells. The area inside the collar appears to be provided with a 
sphincter membrane. 
Fossil Sponges of Flint Nodules.* — Mr. J. A. Merrill has made an 
investigation of the fossil sponges of the flint nodules in the lower 
Cretaceous of Texas. The minute structure of the Cretaceous flints of 
America does not seem to have been as yet studied except in a general 
way, and nothing whatever has heen published on the microscopic 
organisms composing them. The flint nodules examined varied greatly 
in shape and size, and to some extent in hardness. The different kinds 
of sponges found varied so much, and were so much mixed that it is 
difficult to speak with certainty about the depth of the ancient Cretaceous 
sea. Geodict is fully represented, but though it, like Stauractinella , is a 
deep-sea sponge, both are also found in shallow water. The appearance 
of the nodules seems to indicate a very peculiar combination of circum- 
stances which exist but once in a great cycle of changes. From its 
proximity to known shore lines we may judge that the formation was 
not in the deepest sea, but from the forms of animal life preserved in 
it we may conclude that it was beyond the continental shelf, or in 
other words, in water deep enough to secure the necessary conditions 
for long periods of time. 
Protozoa. 
Nettle-threads of Paramsecium.j — The late Prof. J. A. Ryder 
reviewed the conclusion of Allman, that these discharged threads are 
of the nature of defensive organs, and that they are not identical with 
the cilia which thickly clothe the organism. Allman’s views have been 
generally accepted by naturalists. Ryder found that if a pretty strong 
solution of tannic acid is used the threads become entirely detached 
from the body of Paramsecium, if the reagent is allowed to act long 
enough. The tannic acid acts, in short, as a sort of depilatory, 
removing, apparently, every vestige of cilia from the creature. This 
singular power of tannic acid gave rise to grave suspicions as to the 
truth of the statement that the threads developed by tannic acid on the 
surface of Paramsecium are something different from the cilia. By his 
lately described method of imbedding small objects in paraffin J he 
obtained a number of serial sections of Paramsecium no more than 2 • 5 //. 
* Bull. Mus. Comp. Zool., xxxviii. (1895) pp. 1-26 (1 pi.). 
f Proc. Acad. Nat. Sci. Philad., 1895, pp. 167-70. 
X See this Journal, ante , p. 379. 
2 u 2 
