SUMMARY OF CURRENT RESEARCHES. 
601 
Dr. Cb. Fore * lias experimented on tbe influence of the temperature 
on tbe incubation of bens’ eggs. 
(1) At 38°, 20 were normal out of 24 = 83 • 33 per cent. 
„ 41°, 3 „ „ 24 = 12-5 
(2) „ 38°, 12 „ „ 18 = 66-66 „ 
„ 40°, 2 „ 18 = 11-11 
( 3 ) 
38°, 
39°, 
30 
16 
42 
42 
= 71-08 
= 38-09 
And so on with other experiments. Below 37° tbe number of develop- 
ments diminished, 59*45 per cent, at 36°, 56*52 at 35°, 41*66 at 34°. 
Tbe influence of alcoholic vapour increased in effect on each side of 38°. 
Tbe general conclusion is that 38° is tbe optimum temperature during 
tbe early days of incubation, and it is also most favourable for tbe resist- 
ance of injurious influences which may have operated before incubation. 
This has its bearings on “ tbe prophylactic hygiene of degeneration.” 
Dr. F. Braemf has some interesting suggestions in regard to tbe 
influence of pressure on cleavage. Tbe results reached by Pfliiger, 
Roux, and Driescb show that tbe segmentation-spindles always lie at right 
angles to tbe direction of greatest pressure, tbe long axis of tbe spindle 
seeking tbe direction of least pressure. In fact, tbe disposition of tbe 
spindles conforms to tbe conditions of least resistance ; the cells are so 
disposed that they secure tbe greatest freedom for expansion. This is 
complicated, however, by tbe fact that mere contact, as well as pressure, 
appears to have its effect. What Braem does is to apply tbe results of 
experiment to tbe elucidation of normal cleavage, showing bow tbe suc- 
cession of events in tbe development of Synapta is influenced by tbe 
pressure of tbe egg-membrane on tbe blastomeres and by their pressure 
on one another. He tries to explain, for instance, bow a blastosphere 
stage is reached. 
An Abnormal Human Embry 04 — Sig. C. Giacomini adds a thir- 
teenth case to bis important series of abnormalities. He describes a 
defect in tbe development of tbe amnion, in tbe bead-fold, and a corre- 
lated atrophied condition in tbe embryo. 
Origin of the Scleroblasts.§ — Dr. H. Klaatsch makes an important 
contribution to our knowledge of osteogenesis. From a study of tbe 
development of tbe placoid scales in Mustelus and other Selacbii, be 
comes to tbe conclusion that the scleroblasts arise from tbe ectoderm. 
They are derived from tbe same material as that which forms tbe enamel. 
Gradually tbe originally homogeneous rudiment is separated into a part 
previously called mesodermic and a part which remains continuous with 
tbe ectoderm. Tbe separation begins from tbe centre, and for a long 
time there remains a peripheral portion at tbe outer margin of tbe fold 
which serves as a germinal layer for scleroblasts and continues to 
furnish new material. Klaatsch extends this result to tbe development 
of teeth in Mustelus , and to tbe horny rays in tbe fins of Selachians. In 
* Journ. de I’Anat. et de Physiol., xxx. (1894) pp. 352-65. 
t Biol. Centralbl., xiv. (1894) pp. 310-53 (5 figs), 
j Atti R. Accad. Torino, xxix. (1893-4) pp. 638-53 (1 pi.). 
§ Morph. Jahrb., xxi. (1894) pp. 153-240 (5 pis.). 
2 z 
1894 
