ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 213 



integument becomes raised above the bead, forming a serous cavity — - 

 tbe " supra-ccpbalic sinus" — wbicb appears to serve as a float, so as 

 to keep tbe embryos at tbe surface of tbe water. Tbe embryos swim 

 horizontally, but wben at rest bave an oblique position, tbe tail 

 pointing backwards and downwards. It is found tbat if tbe sea-water 

 becomes less dense tban normally, tbe eggs sink and die, sbowing 

 that the cod's eggs, in order to live and develope, float at tbe surface. 



Conditions of Bastard Fertilization.* — Profs. 0. and E. Hertwig 

 find tbat tbe success or non-success of bastardation does not ex- 

 clusively depend on tbe degree of systematic relationship between the 

 crossing species ; this has also been observed by Prof. Pfliiger for 

 Amphibia. There does not seem to be reciprocity in the cross-fertili- 

 zation of two sj)ecies of Eehinoids, any more than of Amphibians ; 

 there are also possible grades ; thus, while ova of ErJiinus microtuher- 

 culatiisare almost always fertilized by spermatozoa of Strong ylocentrotus 

 lividus, tbe reverse is hardly ever successful. Ova of *S^. Uvidiis are 

 not to be fertilized by spermatozoa of Arhacia pustulosa, but the eggs 

 of the latter are often fertilized by the sperm of the former. The 

 condition of the products is of importance, fresh ova being often less 

 successfully bastardated tban those whose vital energy has been 

 lowered by some means ; there is, in fact, a miniviiim and an optimum 

 of capacity for bastardation ; this was well seen by dividing the ova 

 into groups, and fertilizing them under different conditions. In 

 Eehinoids there is no visible difference in the form of spermatozoa, 

 and tbe causes of failure or success must be looked for elsewhere ; it 

 depends on the constitution of the genital products ; complete fertility 

 or sexual affinity only obtains between products of one and the same 

 species ; there reside in the egg-cell regulative forces, which guarantee 

 the normal course of fertilization ; these diminish in power with the 

 vital energy of tbe cell. 



Continuity of the Germ-plasma considered as the basis of a 

 theory of Heredity.f — Prof. A. Weismann's essay f on germ-plasma 

 is reported on by Prof. H. N. Moseley ; it deals with the fundamental 

 question, " How is it that a single cell of the body unites within itself 

 the entire tendencies of inheritance of the whole organism." Prof. 

 Weismann answers this question by supposing that tbe germ-cells 

 arise as far as their essential and characteristic substance is con- 

 cerned, not at all out of the body of the individual, but direct from 

 the parent germ-cell. Tbe germ-jilasma is regarded as a substance 

 of peculiar chemical or even more special molecular composition 

 which passes over from one generation to another ; at every onto- 

 genesis a portion of tbe specific germ-plasma which the parent e«g- 

 cell contains is not used up in producing the offspring, but is reserved 

 uncbanged to produce the germ-cells of tbe following generation ; in 

 fact tbe germ-cells are regarded as separate from the entirety of cells 

 composing the body, and are related to one another as are a scries of 



* Jenaische Zeitsclir. f. Natuiwiss., xix. (1SS.5) pp. 121-G5 • and Supp i 

 (188.5) pp. 72-6. ' 



t Nature, xxxiii. (1885) pp. 154-7. % Svo, Jcmi, 1885, 122 pp. 



