Jan. 29, 1874J 



NA TURE 



247 



HA ECKEL ON INFUSORIA 



T N this communication* Prof. Haeckel discusses the dift'e- 

 -'■ rent views which have been entertained as to the struc- 

 ture of the Infusoria, and adopts that of Prof. Siebold, that 

 they are unicellular. This constitutes in his opinionafunda- 

 mental distinction betweent hem and the rest of tlie animal 

 kingdom, although, strictly speaking, some species, as for 

 instance, Loxodcs rostrum, and Eiichelys gigtis, have 

 more than one nucleus, and must, therefore, be regarded 

 as physiologically consisting of more than one cell. 

 Prof. Haeckel, however, does not attach much importance 

 to these exceptional cases, because the multiplication of 

 the nuclei involves little change of organisation in other 

 respects. 



The difficulty of conceiving a single cell with such 

 complex properties becomes lessened, if we remember the 

 nerve-cells of the higher animals, the thread-cells of 

 many Acalepha;. 



Considering, then, that the true Infusoria are unicel- 

 lular, as first maintained by Prof. Siebold in 1845, Prof. 

 Haeckel denies that they have any near connection with 

 either Ccelcnterata or the worms. In all the higher groups 

 of the animal kingdom the organism is multicellular, and 

 develops itself from the original egg-cell by the charac- 

 teristic process of segmentation, and the cellular mass 

 thus formed differentiates itself into two epithelial 

 layers, from the inner one of which the digestive canal, 

 with all its appendages, develops itself ; while from the 

 outer layer are formed the skin, nervous system, &c. 

 In his monograph of the Calcareous Sponges, Prof. 

 Haeckel has developed his views of the relations of these 

 two primary layers in the principal groups of animals, and 

 from this fundamental homology has enunciated the theory 

 of a common original form, which he proposed to call 

 " Gastraea," and from which all the higher forms of 

 animals are derived. This theory, which he calls the 

 Gastrcea theory, is based upon the consideration that all 

 the six higher animal classes, from the sponges to the 

 lowest vertebrates, pass through a similar stage of devel- 

 opment, which he proposes to call the Gastrula stage, 

 and which he considers to be the most important 

 and instructive embryonal form of the animal king- 

 dom. In the calcareous sponges, for instance, this 

 Gastrula law forms a simple generally egg-shaped body, 

 surrounding an ample hollow, the primitive stomach, 

 or digestive cavity, and with an orifice at one 

 end, the primitive mouth. The wall of the digestive 

 cavity consists of two layers, the entoderm, and the ecto- 

 derm, which, as Prof Huxley was the first to point out, are 

 homologous with the outer and inner layers ol the vertebrate 

 embryo. Similar larva; occur in other sponges, and in many 

 zoophytes, while as examples of embryonal forms in other 

 groups he refers to the researches of Kowalevsky in 

 Phoronis, Sagitta, Euaxes,' Ascidia, &c. ; and of Ray Lan- 

 kester in MoUusca. He considers that the larval forms 

 of Arthropods can be reduced to the same type ; and 

 finally that the researches of Kowalevsky have shown 

 that the same is the case with the lowest vertebrata 

 (Amphioxus). The Infusoria, on the contrary, have no 

 yolk-segmentation, no blastoderm, and consequently 

 nothing which corresponds to the Gastrula stage, nor any 

 homologuc of the digestive cavity of other animals. 

 The resemblance of many ciliated larvae to the Infusoria 

 is therefore merely superficial, the latter being unicellular, 

 the latter multicellular. He regards this difference as so 

 fundamental that he proposes to divide the animal king- 

 dom into two great groups, the Protozoa, and the Metazoa, 

 Blastozoa, or Gastrozoa. The Metazoa, to use his first 

 name, he again divides into two ; the Zoophytes, or Cce- 

 lenterata on one side, and the Worms, from which again 

 the Molluscs, Echinoderms, Arthropods, and Vertebrates 

 have sprung, on the other. 



* Zur morpholrtsie der Infusorien. Sep. Abdruck aus der Jenaischen 

 ZeitscrKt. 13d. vii. 



LECTURE EXPERIMENT 

 'T'HE ordinary experiment described in books for 

 -■■ demonstrating the heating of a body of fluid by 

 convection currents consists in throwing bran into a vessel 

 of water, to the bottom of which a source of heat is after- 

 wards applied. Mr. Clowes's experiment, given in Nature, 

 vol. ix. p. 162, is no doubt more eftective. I have, however, 

 found that the ordinary experiment admits of being made 

 quite satisfactory for the purpose of clear demonstration, 

 and the hint may be useful to those to whom it has 

 not already occurred. 



Take a large beaker filled with water, and introduce 

 down to the bottom the end of a burette filled with a 

 strong indigo solution and closed at the lop by the 

 finger. If necessary, the solution may be driven out by 

 the apphcation of the mouth to the other end, and gently 

 blowing. The burette must be carefully withdrawn without 

 producing upward currents ; this can be easily managed 

 with a little care. The dark fluid now lies at the bottom 

 of the clear water, with which, during a time sufficient 



for the experiment, it does not appreciably mix. But 

 when a spirit lamp is applied it rises in slender streams, 

 which can be rendered very visible by placing a sheet of 

 white paper behind the beaker. W. T. T. D. 



A SCIENCE LECTURE AT THE CHARTER- 

 HOUSE 



A LECTURE on one who was once a Brother of the 

 Charterhouse, and who laid the foundations of scien- 

 tific electricity, could not fail to be of interest when deli- 

 vered within the walls of that building, where indeed 

 many of the experiments of the original investigator in 

 question were conducted. This pleasant duty devolved 

 on Dr. Richardson on Thursday, January 22, when he 

 gave to the brethren of the Charterhouse, and to many 

 eminent friends, an experimental demonstration of the 

 work of the early electrician, Stephen Gray. 



The lecturer opened his discourse with an exposition 

 of the personal history of Mr. Gray ; of this, he said, he 

 could gather little. He discovered Gray first at Canter- 

 bury, in 1692, making an observation of a mock sun, in 

 the afternoon of February 6. At this time Gray was evi- 

 dently engaged on physical and astronomical research. 

 In i6g6 he was busy constructing a water microscope ; 

 in 1698 he was engaged miking a microscope with a 

 micrometer for measuring the height of mercury in the 

 barometer more exactly ; in 1699, on April 7,between 4P.M. 

 and 5 p.m., he was observing an unusual parhelion and 

 a halo ; in 1701 he was studying the fossils of Reculver 



