154 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
the processes, for it is likely that the needles supply some stimulus to 
growth. The author then discusses the occurrence of fused pluteus 
larvae and the origin of blastulae from parts of ova. Experimenting 
further with potassium chloride mixtures, he evoked larvae with an 
exaggerated tuft of cilia at the animal pole, but he failed at Naples to 
repeat with success this experiment which he had made at Trieste, and 
believes that the failure was due to the different temperature conditions. 
By adding lithium salts to the water strange results were produced. 
The normal blastula elongates and divides into two vesicles, one thin- 
walled, the other thick-walled; the thin portion Eerbst has reason to 
call the “ gastrula-wall portion,” the thick portion is the “ archenteric 
portion ” ; they differ also in pigmentation and in their cilia ; calcareous 
needles were rarely formed ; a special connecting region arises between 
the two main portions; and other peculiarities were exhibited before 
death put a stop to the strange development. The experimenter believes 
that plutei would after all have developed out of some, had they lived. 
By adding more and more lithium salt he was able to reduce the 
“gastrula-wall portion” almost to nil. The thick-walled portion is 
really a protruded archenteron ; the connecting portion is the hind- gut 
of the pluteus. It is interesting to notice that the influence of the 
various salts of lithium (chloride, nitrate, bromide, and iodide) is 
inversely as their molecular weights, the chloride being most powerful, 
the iodide least powerful. The results go to show that the production 
of the abnormalities in development is due not to a direct chemical 
reaction, but to the changed physical conditions, and especially to the 
changed osmotic pressure of the medium. 
Yolk-cells and Yolk Segmentation.* — Herr Hs. Virchow continues 
his discussion of the vertebrate yolk-organ. It is either a diverticulum 
of the mesenteron (lamprey, sturgeon, amphibians) or a sac with a duct 
(Selachii, Teleostei, Amniota). The endoblast of the yolk-organ occurs 
in two forms — peripheral layer and internal cell mass, epithelial cells 
and yolk-cells. In discussing the homology of various yolk-organs, 
attention must be directed to the topographical relations, to the primary 
circulation, and to the parietal appendages (if any). There are two 
great types, that of Selachii- (and Teleostei), and that of Amniota (and 
Amphibia). Yolk-cells are either true cells or only cell- territories 
(merocytes). Yolk-segmentation differs from typical segmentation in 
three ways : — The resulting cells are not again divided, they have from 
the first the size of tissue-cells, they are from the first yolk-cells and 
nothing more. Nuclei are distributed in the yolk, and around these 
nuclei cells are defined off. A typical illustration is found in Ichthy- 
ophis. “ Deferred segmentation,” which occurs in reptiles and slightly 
in birds, is not to be confused with yolk- segmentation. Yolk-segmen- 
tation leads to the formation of yolk-cells and to nothing else ; but 
yolk-cells may also arise by typical segmentation or from yolk-free 
cells. 
Development of Auditory Ossicles.| — Dr. Baumgarten has investi- 
gated this in a human embryo. He has followed Born and Strasser in 
* Verhandl. Anat. Gesell., vi. (1892) pp. 209-20. 
t Archiv f. Mikr. Anat., xl. (1892) pp. 512-30 (1 pi.). 
