744 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
effected by tbe activity of the same calciferous cells, with which new 
cells become connected. “ The calcifying matrix, originated from the 
ectoplasm of many calciferous cells, predetermines the form of the 
increasing deposit, and gives rise to the organic substance in the deposit 
as well as to the thin coat or membrane which invests it. 
In the development of the Pluteus (7) three successive stages are to 
be distinguished by a difference in the number of the centres of calcifi- 
cation and by a gradual increase in the number of rods and arm-like 
appendages. So few pluteus-larvae are as yet well known that it is 
impossible to make comparisons which will give any general results of 
value ; but it may be said that the Clypeastroids have a pluteus which 
is rounded posteriorly, is devoid of epaulettes and a terminal arm, and 
has but eight arms. 
Finally, (8) the development of the young is considered; in the 
oldest example, which was about two months old, the bilateral symmetry 
is very striking ; the spines are proportionately long ; the buccal mem- 
brane is just pierced, but there is as yet no anus ; and the dorsal region 
is strengthened by a large calcified perforated plate which covers the 
greater part of the back. This plate is derived from the central part of 
the odd dorsal rod which characterizes the fully mature pluteus. In 
order, indeed, to understand the growth of the calcareous deposits in 
general and all the changes which take place in connection with it, we 
must note that a re-deposition of calcareous matter must occur side by 
side with an absorption, just as in the case of bone; in other words, 
while a part of the wandering cells are employed in building up, other 
so-called phagocytes devour and destroy such parts of the plates, rods, 
&c., which are useless or impede the advance of a normal development. 
Abnormal Specimen of Antedon rosacea.* — Mr. H. C. Chadwick 
has met with a specimen of this Comatulid in which there was a super- 
numerary disc attached to the normal one by a sort of stalk ; of this he 
was able to make an unbroken series of sections. These showed that 
the body-cavities of the two discs communicated freely with each other, 
while the alimentary canals were quite distinct. The skeletal and axial 
nervous systems present in the normal disc are quite absent from the 
supernumerary. 
Discussing the explanations that may be given as to the origin of 
the latter, he points out that against the hypothesis of budding there is 
the entire absence of arms, and of skeletal and axial nervous systems in 
the supernumerary disc; the suggestion (due to Prof. Mi lues Marshall) 
that the phenomenon is the result of incomplete evisceration receives 
more favour. 
Notes on Holothurians.j — Dr. E. von Marenzeller thinks that the 
Cotton-spinner ( Holothuria nigra ) is identical with H. Forskalii of the 
Mediterranean, as is also H. cataniensis and Stickojpus Selenkse ; in the 
Atlantic Ocean H. Forskalii does not attain so large a size as in 
the Mediterranean. Cucumaria Koellikeri is also found in the Atlantic. 
The author thinks that Edward Forbes’ Psolinus brevis is the Cucumaria 
* Ann. and Mag. Nat. Hist., xii. (1893) pp. 195-8 (1 pi.). 
f SB. Akad. Wiss. Wien, 1893, pp. 107-9; see Ann. and Mag. Nat. Hist., xii. 
(1893) pp. 334 and 5. * 
