182 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
also a Dipylidium larva. The sliape of the rostellum, the number, 
shape, and arrangements of the hooklets seem to decide the question. 
Echinoderma. 
Formation and Absorption of Skeleton in Echinoderms.* — Prof. 
H. Theel has an interesting note on this subject. After pointing out 
reasons for doubting the accuracy of Chun’s results he describes his new 
observations on the process of absorption in living larvae. The cells 
which effect the absorption and destruction of the larval skeleton are 
hardly to be distinguished from those which deposit inorganic substances, 
and they probably have their origin from them. Their activity almost 
conveys the impression that the process of absorption demands - much 
more intense labour on the part of the cell than that of deposition. They 
give off pseudopodia which become extended into long, slender filaments ; 
these branch and anastomose with each other, as well with the pro- 
trusions of other cells, and in this way there is formed a network of 
fine and wide meshes. The pseudopodia change incessantly, and the 
appearance of the cell is constantly altering ; soon the pseudopodia may 
be observed to be withdrawn, and as the network which they formed 
disappears other protrusions give rise to new sets of meshes. When 
a cell begins to exercise its absorbent influence on a calcareous body 
it extends and flows round and over it so as to take it wholly into its 
protoplasm. For this reason the granular main portion of the cell may 
be seen to move incessantly, gliding slowly along the swallowed spicule 
until nothing remains of it. Prof. Theel has never seen the cell leave 
the spicule till absorption was completed. He thinks that the dissolved 
salts are gradually transferred through the pseudopodia to neighbouring 
cells, which either retain them till they are wanted, or use them imme- 
diately as materials for building up new calcareous bodies essential for 
the growing Echinoderm. The process of absorbing calcareous bodies 
commences when the skeleton becomes unsuited for further evolution 
of the larvae, and when the sea-urchin, in process of growth, is in need 
of calcareous salts in great quantities, that is to say, when the pluteus has 
attained its mature state. At this period numerous organs all requiring 
abundance of calcareous salts begin to arise almost simultaneously, and 
we see the advantantage of a supply of calcareous substances in reserve 
within the body. This process of absorption goes on very rapidly, for 
instance, a calcareous plate almost too large for the body of a cell can 
be completely dissolved within two hours ; so that the dissolving fluid 
must be present in great abundance. 
Distribution of Echinoderms of North-eastern America.! — Prof. 
A. E. Yerrill reports that about 200 species of Echinoderms are now 
known from the Atlantic Ocean, adjacent to the North American coast. 
Of these over 100 have been discovered in recent years since deep-sea 
dredging was undertaken. It was found that the abyssal genera and 
families are mostly very widely diffused over the three great ocean basins, 
while the species belonging to them are generally restricted in range to 
particular regions, or to a single ocean. The genera and species that 
* Ofv. K. Yet. Akad. Fork., li. (1894) pp. 345-54 (3 fc figs.). 
f Amer. Journ. Sci., xlix. (1895) pp. 127-44. 
