481 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
The author traces the genital cells back to the epithelium lining the 
canal which represents the most aboral portion of the dorsal organ, 
while this last has a cavity which, at an early stage, communicates with 
the coelom ; its epithelium, therefore, is peritoneal epithelium. From 
this it follows that in both Amphiura and Asterina the genital cells are, 
ultimately, derived from the peritoneum, or, in other words, they have 
the same origin as the sexual cells of all Coelomata. 
Cleavage of Eggs of Arbacia.* — Dr. J. Loeb has experimented on 
the dividing eggs of Arbacia by exposing them to water containing more 
or less than the normal amount of sodium chloride. If the irritability 
of the protoplasm of the egg be reduced by reducing the amount of water 
contained in it, the nucleus can segment without segmentation of the 
nucleus. If we now increase the quantity of water the protoplasm at 
once divides into about as many cleavage cells as there are preformed 
nuclei. The effect of salt is not to destroy but to suspend the cleavage 
phenomena ; the longer eggs are kept in concentrated water the more 
numerous are the cleavage cells formed all at once when the egg is 
returned to normal water. It would appear that the nuclei increase in 
numbers in salted sea-water, though no cleavage furrows are visible on 
the outside of the egg, but this increase is not always accompanied by a 
normal separation. 
The normal source of the stimulus which the abstraction of water is 
supposed to render no longer efficient to produce cleavage is supposed 
to be the nucleus, but the nature of this stimulus is unknown ; there are 
some reasons for believing it to be of a chemical nature. 
On the other hand, the protoplasm has some influence on the nucleus ; 
and it is suggested that the intracellular pressure which determines the 
form of the cells also fixes the direction of the nucleus. 
Crinoids from Sahul Bank.t — Prof. F. Jeffrey Bell has a note on 
a small collection of Crinoids from the Sahul Bank, North Australia. 
The only stalked form in the collection is Metacrinus interrupts P.H.C., 
taken from a telegraph wire from about as many degrees south of the 
equator as the type was north of the line. Evidence is afforded as to 
the very considerable range of variation in the length of the cirri of 
Antedon longicirra P.H.C. ; A. Wood-Masoni is a new species of Car- 
penter’s Spinifera- group ; A. patula P.H.C. was also in the collection, 
and it is hinted that it, A. flexilis and A. robusta, which were all taken at 
the same station by the * Challenger,’ may not be as distinct as is at 
present supposed. 
Holothurians from the Eastern Pacific.^ — Prof. H. Ludwig has a 
preliminary notice of the Holothurians collected by the ‘ Albatross ’ 
deep-sea expedition to the Eastern Pacific. Forty-six species belonging 
to twenty-eight genera were collected ; the most interesting forms are the 
representatives of a group intermediate between the Aspidochirotas and 
the Elasipoda and a rare Holothurian adapted to a pelagic life. 
Several examples were obtained of Theel’s Pseudostichopus mollis ; 
the investigation has resulted in an alteration of the generic diagnosis. 
* Journ. Morphol., vii. (1892). See Amer. Natural., xxvii. (1893) pp. 398 and 9. 
t Journ. Linn. Soc. London, xxiv. (1893) pp. 339-11 (2 pis.). 
j Zool. Anzeig., xvi. (1893) pp. 177-86. 
