516 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
stage of maturation readied by the egg. Miss Foot’s observations 
suggest that both the cone and the attraction-sphere are expressions of 
a definite effect produced upon the cytoplasm by the entrance of the 
sperm, the phenomena differing in that the anterior end of the head of 
the spermatozoon produces a cone, whereas the middle piece produces 
the attraction-sphere. 
Directive Influence of Gravity on Development.* * * § — Prof. 0. 
Schultze furnishes some new evidence of this. By three methods he 
eliminated the normal action of gravity on developing frog ova, and all 
came to nothing. He therefore reaffirms with confidence his previous 
conclusion that the directive action of gravity on the egg of the frog is 
an essential condition of normal development. 
Historical Note as to Polar Bodies.f — Prof. E. van Beneden re- 
cently stated that the theory of polar bodies as morphologically equiva- 
lent to ova was first formulated by Mark in 1881, and soon afterwards 
by Biitschli. He based his statement, which was quite an obiter dictum, 
on E. B. Wilson’s book on the Cell (p. 175). Prof. A. Giard J points 
out, however, that the theory was advanced by himself in 1876. Van 
Beneden makes the correction, but he does not in the least agree with a 
further statement made by Giard, that the polar bodies are formed by a 
true typical mitosis. As is well known, van Beneden has always in- 
sisted upon the differences between typical mitosis and the divisions 
which give rise to polar bodies. 
Lateral Sensory Rudiment in Salmon.§ — Messrs. H. Y. Wilson and 
J. E, Mattocks have added the salmon to the list of forms in which a 
common lateral Anlage occurs. It divides, as in Serranus (where Wilson 
first discovered it), into three parts, the middle becoming the auditory 
sac, the posterior the rudiment of the lateral line, and the anterior 
remaining as a very noticeable thickening situated above the anterior 
gill-clefts. The original Anlage is in the salmon, as in Selachians, a 
thickening, and not an invagination. 
Development of Selachii.|| — Prof. C. K. Hoffmann continues his 
studies on the development of Selachians, discussing the fourth and fifth 
paiingenetic somites of the head, the sixth palingenetic somite and the 
four camogenetic protovertebrae or occipital somites, the ventral nerve- 
roots of the head-somites, and the development of the trochlear nerve. 
Early Development of Cestracion.^T — Prof. W. A. Haswell describes 
the early history of the blastoderm in Heterodontus ( Cestracion ) PJiillipi 
up to the time of the enclosure of the archenteron. As this Elasmobranch 
was represented by near relatives as far back as the Carboniferous 
period, it was hoped that the embryonic development might exhibit some 
important primitive features. So far, however, this expectation has not 
been fulfilled. “ What impresses one most in the results is the extra- 
ordinary persistency of certain characteristics which are not known to 
* Yerli. Anat. Ges. Anat. Anzeig., Bd. xiii. Erganz.-Heft, pp. 109-16. 
t Bull. Acad. Roy. Belg., xxxiv. (1897) pp. 21-4. 
x C.R. Soc. Biol., iv. (1897) p. 549. 
§ Anat, Anzeig., xiii. (1897) pp. 658-60 (2 figs.). 
|| Morph. Jahrb., xxv. (1897) pp. 250-304 (2 pis. and 9 figs.). 
1 Proc. Linn. Soc. N.S.W., xxii. (1897) pp. 96-103 (2 pis.). 
