242 Prof. H. Fol on the Family Tintinnodea. 



with such rapidity, and only stop when they contract into a 

 shapeless mass ? 



The test of our animals is composed of a hard slightly 

 elastic material, which, hoAvever, breaks when the pressure is 

 slightly increased. This substance resists acids even when 

 tolerably concentrated, and presents no evolution of gas ; 

 therefore it is not an earthy carbonate. It burns away en- 

 tirely at a dull red heat ; hence it is not silica. It resists for 

 a long time the action even of tolerably concentrated alkalies ; 

 consequently it is not a horny substance. There remains 

 only chitine, to which we are led by the method of exclusion. 

 Leaving the description of the different forms observed 

 until we come to speak of the genera and species, I shall only 

 remark that the test generally presents two distinct layers, 

 which, however, to all appearance, are of the same chemical 

 composition. All the tests hitherto observed by various 

 authors and by myself may be referred to three types which 

 seem at the first glance very distinctly marked — namely, 

 smooth tests, tests garnished with adherent foreign particles, 

 and latticed tests. However, there are species which esta- 

 blish the transition between the smooth tests and the tests 

 with adherent particles ; and on the other hand, among the 

 latticed tests, that wliich I have had the opportunity of ob- 

 serving was continuous, and only hollowed out by a number 

 of small cavities on its outer surface. It was not perforated, 

 which approximates it to certain smooth tests presenting 

 patterns on their outer surface. 



Notwithstanding all my researches, I have not succeeded in 

 observing the reproduction of these animals. On the other 

 hand, I have very frequently observed the initial act of the 

 sexual reproduction of Infusoria, namely conjugation. It is 

 well known that the Infusoria, after arriving at a certain point 

 in their cycle of development, unite two and two and become 

 more or less intimately amalgamated. The nuclei of the two 

 copulated individuals also become amalgamated, and appear 

 to exchange a part of their substance. After this act, which 

 in its essential features corresponds to the fecundation of the 

 Metazoa, the two individuals separate, and each of them re- 

 produces by a phenomenon of total or partial scissiparity. 



In the 2 mf inn/' the presence of the test is not an obstacle 

 to conjugation. The individuals do not quit their tests in 

 order to unite ; they amalgamate by the margin of the peri- 

 stome. The point of union is absolutely constant ; it is situ- 

 ated in the vicinity of the mouth, but a little to the left of the 

 latter, in such a way that two individuals in conjugation 

 always form a perfectly symmetrical figure (PI. XVII. fig. 3). 



