ZOOLOGY AND BOTANY, MIOROSCOPY, ETC. 541 



instead of being obliged to grow up to maturity before arriving at this 

 stage. 



Thus all cells may be regarded as larval Protozoa, and eggs and 

 spermatocysts as encysted larval forms, the spermatozoa being equi- 

 valent also to larval forms which have inherited the tendencies of the 

 mature forms in the Protozoa at the earliest stages. Thus the origin 

 of the tissues in the Metazoa is in exact accord with the law of con- 

 centration and acceleration in heredity. The cells are larval, which, 

 in accordance with this law, have inherited the characteristics and 

 tendencies of their adult ancestors in their earliest stages. The three 

 layers can be accounted for as larval characteristics inherited from 

 colonies of Infusoria flagellata, which had two forms (protective and 

 feeding zoons), and then three (protective, feeding, and supporting), 

 these corresponding to ectoderm, endoderm, and mesoderm. 



Development of Proto vertebrae.* — H. Fol, from a number of 

 experiments on the order of appearance of the protovertebrae of the 

 common fowl, comes to the conclusion that " the first-lormed somites 

 of the body appear to be the most anterior of the whole series, and 

 that they correspond, perhaps, to the cephalic region ; the long series 

 of protovertebrae are formed successively from before backwards." 

 Thus the vertebrate embryo commences, so to speak, as a head only, the 

 rest of the body appearing by degrees. 



Experiments in Arrested Development. f— Another communication 

 by M. Fol deals with some observations made by himself and S. 

 Warynski which tend to confirm a previous discovery, that by 

 momentarily heating the left side of an embryo chicken, a complete 

 visceral inversion is obtained. The experiments consisted in pressing 

 with the blade of a scalpel a portion of the embryo without injuring 

 the vitelline membrane ; by so doing, the development of that ])ortiou 

 lying outside the line of pressure was completely stopped. The de- 

 velopment of the left side of the embryo was hindered by separating 

 it from the afferent portion of the vascular area, and it appears to be 

 by an arrest of development of the left side that a visceral inversion 

 is produced, " from which it may be concluded that this side ought to 

 predominate to bring about the normal torsion." 



Morphology of the Directive Corpuscles.^ — 0. Biitschli points 

 out that, for a satisfactory comprehension of the morphological 

 BJgnificauce of the directive corpuscle, it is necessary to bear in mind 

 the mode of sexual rei)roduction in the colonial Volv()cinea3, a group 

 of the Flagellata, which not only by their structure, but also by the 

 characters of their method of reproduction, approach most closely to 

 the Metazoa, even though their mode of nutrition is vegetable in 

 charact(jr. The simplest case of sexual reproduction has been made 

 known to us by the researches of Pringshoim on Pandoriiia. 



In it, at certain times, the cells of a colony give rise by successive 



• Arch. Sci. Phyw. et Nat., xi. (IHHl) p. 104. 



t Ibi<l., ]>. 105. 



: Hi.jl. CtiitralljI., iv. (1881) pp. 5-12. 



