706 SUMMARY OF CURRENT RESEARCHES RELATING TO 



we find that in sixty-six species of animals the eggs gave oJ0F two primary 

 polar globules, and that for all these the necessity for fertilization was 

 certain, and in most of them fertilization was observed. On the other 

 hand wo know of fourteen species, the ova of which undoubtedly pro- 

 duced only one polar globule, and these were without exception partheno- 

 genetic. We cannot, therefore, but conclude that eggs that require to 

 be fertilized form two polar globules, and parthenogenetic eggs one. 

 The significance of these facts has already been pointed out by Prof. 

 Weismann.* 



Origin and Significance of the so-called free Nuclei in the 

 Nutrient Yolk of Bony Fishes.j — Prof. C. K. Hofiinann has a paper, 

 largely critical and controversial, in wliich he deals with the observations 

 of cmbryologists who have treated of the matter since the time when 

 he asserted that these nuclei arise directly from the first cleavage- 

 nucleus. 



Resemblance of Ovarian Ova and the Primitive Foraminiferat 

 — Prof. J. A. Ryder remarks that upon cutting sections of nearly mature 

 ovarian ova with tlieir investing membrane, zona radiata, in place, it 

 was found that in quite a number of cases fine protoplasmic processes or 

 pseudopotls extended from the peripheral layer of protoplasm of the egg, 

 through its capsule or zona, and joining the cells of the granulosa or 

 discus proligerus. This arrangement reminded one forcibly of the 

 filamentous pseudopods extended from a Hcliozoon, or of the slender 

 pseudopods extended through the perforations in the walls of the single 

 chambers of Glohigerina. This resemblance is all the more suggestive 

 if one will compare a section of one of the chambers of a Glohigerina 

 made through the calcareous shell and its contained protoplasm with 

 a similar section through the ovum of the Gar pike, where the zona is 

 formed of pillars of homogeneous matter. 



Such prolongations of pseudopods through the investing zona radiata 

 in the case of many species of animal forms show fairly well that this 

 must be the principal means by which new matter is taken up from 

 without and incorporated, as there is no direct extension of the vascular 

 system into the egg by which it can take up nutriment. 



It is thus seen that the early stages of the growing ovum not only 

 resemble some of the lower forms of Heliozoa and Foraminifera as 

 respects the grade of their morphological differentiation, but also as to 

 the mode in which they exhibit their nutritive or physiological activities. 

 This resemblance is still further heightened if a form like Arbulina is 

 compared with certain stages of the development of ova. It is thus seen 

 that in many cases the ovarian germ, at least, passes through a stage 

 which may be morphologically as well as physiologically compared with 

 some of the lowest grades of the Protozoa. 



Inversion of the Germinal Layers in the Shrew.§ — Herr J. Bieh- 

 ringer reports the results of some studies on the development of the 

 germinal layers in Arvicola amphihius Desm. He gives a short summary 

 of previous investigations. 



He begins with the 42-cell stage, a roundish mass without segmenta- 



* See this Journal, 1887, p. 934. 



t Zeitschr. f. Wiss. Zool., xlvi. (1888) pp. 517-48 (1 pi.). 



X Proc. Acad. Nat. Sci. Philad., 1888, p. 73. 



§ Arch. f. Anat. u. Physiol. (Anat. Abth.), 1888. pp. 279-86 (1 pL). 



