ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 761 



following terms: It is the only as yet known continental Poly- 

 thalamian, and in the form of its shell resembles that of the sub-family 

 Eotalinfe of the group GlobigerinaB ; in structure the shell resembles 

 that of Trochammina ; in the structure of its partitions it agrees with 

 the perforate Polythalamia ; in that of the orifices of these partitions 

 with the Lagenidfe ; the chemical constitution is that of Difflugia, 

 Trochammina, and some of the Globigerina, and it closely con- 

 nects the last with the Lagenidae by means of Trochammina and the 

 Eotalinas. 



Nuclear Division in Actinosphaerinm eichhornii.* — E. Hertwig 

 concludes from his observations on the resting nucleus that the 

 coloured constituents of the nucleus (chromatin or nuclein) are not 

 spongy bodies ; all the nuclein is contained in nucleoli, which are 

 stained by reagents. A subject of greater difficulty is presented by 

 the parts which are formed in addition to the nucleoli within the 

 nucleus. These are (1) the granulation which becomes visible on 

 the addition of reagents ; (2) the paranuclear pieces which in the 

 fresh condition are seen to have various forms ; (3) the highly 

 refractive corpuscles; and (4) the nuclear membrane. The first 

 three appear to be referable to a common structure of colourless 

 substance, which may be called paranuclein or achromatin, and 

 which fills up the interspaces between the nucleolus and the nuclear 

 membrane. It may be regarded as due to special thickenings of the 

 achromatic network. The author is acquainted with essentially 

 similar phenomena, which have presented themselves in the nuclei 

 of insects, and of which he will give an account at a later period. 



The mode of division of the nucleus, as seen in Actinosphcerium, is 

 intermediate in character between what is seen in plants and animals 

 on the one hand, and in Protozoa on the other ; in the latter, which 

 approach most nearly the diagrammatic scheme, the biscuit-shaped 

 constriction of the nucleus is most apparent ; internal differentiations 

 of the nuclear substance are either completely wanting, or are nearly 

 fibrillar. (An exception to this is seen in the paranuclei of the 

 Infusoria.) On the other hand, in plants and animals the biscuit- 

 shaped constriction is obscure, the limits of the nuclear substance 

 and protoplasm disappear, and there is a mixture of the two sub- 

 stances. The whole division of the nucleus appears, therefore, as a 

 complicated and extremely regular rearrangement of the nuclear 

 particles, which lead to the important differentiation of achromatic 

 nuclear filaments and of chromatic elements ; the two substances are 

 BO sharply separated that they might be taken for elements which 

 had nothing to do with one another. 



In Aclinosphcerium we have, as in the other Protozoa, those changes 

 in form which the whole nucleus undergoes during division ; but as 

 to its internal structure there are many points in which the nucleus 

 resembles that of animal ova ; a nuclear plate is formed, which divides 

 into lateral plates that separate from one another and the parts of the 

 lateral plates give rise to achromatic filaments. Before the appcar- 



• Jenaisch. Zeitschr. f. Naturwias., xvii. (1884) pp. 490-517 (2 pis.). 

 Her. 2.-V0I.. IV. 3 e 



