ZOOLOGY AND BOTANY, MICROSCOPY, ETC. L63 



the cases in which it is developed, has disappeared as such ; all the 

 following processes, the longitudinal growth of the embryo, the covering 

 of the yolk by the blastoderm ring, the closure of the yolk blastopore, 

 belong to the notogenesis, and we are no more entitled to reckon these 

 processes to gastrulation proper than we are to do that of the covering 

 of the yolk by the entoderm in Sauropsids. 



Early Stages of Fresh-water Fishes.* — F. B. Browne gives a brief 

 account of the early stages in the life-history of the pike, the perch, the 

 bream, the roach, and the stickleback. 



Monstrosities. t — Paul Ernst discusses numerous human monstrosities 

 in the light of experimental embryology and phylogeny. He shows in 

 an instructive way how recent researches on the influence of abnormal 

 conditions on ova and embryos throw light on familiar teratological 

 phenomena in man. There is less light to be got from phylogenetic 

 considerations, but illustrations of arrested development are common. 

 The paper is illustrated by a grim series of plates showing monstrosities. 



b. Histolog-y. 



Structure of Cilia.J — L. W. "Williams has studied the action of cilia,, 

 especially on Gastropoda larva, and has been led to a modification of 

 the theory of their structure. All protoplasmic processes, cilia, flagella, 

 pseudopodia, and Acinetarian tentacles, are of essentially the same 

 structure, and consist of a contractile protoplasmic sheath enclosing 

 a solid or fluid non-contractile core. Primitively the sheath is con- 

 tractile throughout, and is not marked off structurally or functionally 

 from the rest of the ectoplasm. Secondarily the sheath becomes 

 differentiated into contractile and non-contractile portions. 



The contractile protoplasm of velar cilia and ctenophore plates is 

 practically confined to the base of the cilium. Parker has shown that 

 in reversible cilia, e.g. in Metridium, the contractile substance must 

 occur in two bands on opposite sides, and that irreversible cilia have 

 probably only one band. Ballowitz has shown that spermatozoan flagella 

 have a fibrillar axial structure surrounded by a sheath of uneven thick- 

 ness ; others have shown that the axial rod supports an irregular con- 

 tractile protoplasmic sheath. 



The core of the pseudopodium, which is to be regarded as the 

 simplest cilium, is fluid. In higher stages of ciliary development a solid, 

 which is elastic in cilia and flagella and inelastic in pendulous pseudo- 

 podia, replaces the fluid core. 



Development of Cartilage. § — Ed. Retterer finds that in embryonic 

 development the first trabecular of fundamental substance are elaborated 

 by the chromophilous protoplasm of the cellular syncytium which repre- 

 sents the primordium of the cartilage. From their first appearance they 

 show zones or lamellae, alternately light and dark. To begin with, the 



* Trans. Norfolk and Norwich Nat. Soc, viii. (1907) pp. 478-88 (2 pis.). 

 t Verh. Schw. Nat. Ges., 89th Jahres. in St. Gallen, 1907, pp. 129-G9 (19 figs., 

 mostly plates). J Amer. Nat., xli. (1907) pp. 545-61 (2 figs.). 



§ C.K. Soc. Biol. Paris, lxiv. (1908) pp. 3-6. 



