ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 313 



any close relation to the chromatin, is absorbed with the remaining 

 chromatin in the body of the cell. A little yolk is formed diffusely 

 along with chromatin-condensations on the cytoplasm of the ripe ovum. 

 In ForskaJia contorta and AgaJimi rubra there is a filamentous 

 condition of the chromosomes after the last oogonial division ; these 

 become teased out, the chromatin collects in the nucleolus. From the 

 nucleolus there is a diffuse emission of chromatin. After this the 

 chromatin leaves the nucleolus and chromosomes are reconstructed. 

 There is abundant yolk covered over with chromatin-bearing cytoplasm. 

 The author maintains that the chromatin is a cyto-morphological con- 

 ception, which does not always correspond to the same sort of physico- 

 chemical substance. 



Polypodium hydriforme.* — A. Lipin has studied the early stages of 

 this interesting parasite of sturgeon's eggs. A small diploblastic body 

 without tentacles or cnidoblasts (like a barleycorn) occurs in the eggs 

 before they are quite ripe. A closed stolon appears coiled within the 

 barleycorn and gives off buds, which have twelve tentacles and show 

 cnidoblasts. The ectoderm is now internal ; the endoderm external — 

 an adaptation to parasitism. At a later stage re-inversion occurs. It is 

 only after the sturgeon's eggs are laid that a mouth is formed. Free- 

 living forms of Polypodium, with six, twelve, or twenty-four tentacles, 

 succeed one another, multiplying by fission. The endoderm becomes 

 flagellate, and both muscle-fibres and nerve-plexus are endodermic. 



Experiments on Hydra.f — W. Koelitz has studied regenerative and 

 regulative processes in Hydra. Two of his results may be taken in 

 illustration. The regenerative capacity gradually decreases from the 

 oral end towards the basal disk. When a polyp has too many tentacles, 

 e.g. as the result of grafting, the average may be restored by a coalescence 

 of adjacent tentacles, and another good instance of the restitution of the 

 normal is seen when two polyps are artificially united by their oral regions. 



Porifera, 



Division of Collar Cells in Calcareous Sponges. | — Muriel Robertson 

 describes this in Grantia and Sycon. It is a quite typical Metazoan mitosis, 

 but reveals one or two rather primitive features, such as the very slight 

 development of the spireme, the absence of rays from the centrosomes, 

 and the general indistinctness of the chromosomes. The main feature 

 of interest is that the blepharoplast plays the part of a centrosome, and 

 evidence is afforded as to the simple achromatic nature of this substance. 



Structure of Spirastrella.§ — G. C. J. Vosmaer finds that thirty-two 

 of the thirty-four alleged species of the siliceous sponge Spirastrella are 

 referable to one uncommonly variable species, S. purpurea (Lmk.) Rdl. 

 There is a great diversity in external appearance, in the canal system, in 

 the structure of the parenchyma, and in the characteristic spinispirge. 



* Zool. Jahrb., xxxi. (1911) pp. 317-426 (5 pis.). 



■I- Arch. Entwick., xxxi. (1911) pp. 191-257, 423-55. 



X Quart Journ. Micr. Sci., Ivii. (1911) pp. 129-39 (1 pL). 



§ Proc. Sect. Sci. K. Akad. Amsterdam, xiii. (1911) pp. 1139-46. 



June 19th, 1912 z 



