1894. NOTES AND COMMENTS. 5 



so that before two months were up Mr. Chadwick had seven sea- 

 cucumbers instead of three. 



In the twenty-first volume of the Norwegian North-Atlantic 

 Expedition, Dr. D. C. Danielssen tells us that among the specimens 

 of Baihycrinus carpenteri dredged, a large number were found to have 

 thrown off the part of the crown that lay above the basals, and in 

 several instances to have reproduced it again. He further points 

 out that, while the other specimens dredged had genital products 

 developed in their pinnules according to the normal method of sexual 

 reproduction, the crowns that were thus thrown off were sterile; and 

 he suggests that, when the sexual powers of the old crown are worn 

 out, it is rejected, and a new one with fresh powers grown in its place. 

 Now, if we remember that the most recent investigators concur in 

 deriving the genital rachis of the crinoid arm from an extension of 

 the so-called " dorsal organ," which Hes between the basals, then we 

 see that this recuperation of the crown may be regarded as a means of 

 obtaining a fresh extension of this dorsal organ into that part of the 

 crinoid where alone its generative faculty is available for sexual 

 purposes — namely, into the pinnules. This idea certainly coun- 

 tenances Dr. Danielssen's suggestion. At the same time, we must 

 not forget that in certain ophiurids, as Liitken and Cuenot have 

 observed, reproduction by fission only occurs in immature individuals, 

 and sexual reproduction appears to ensue only when this asexual 

 method has been many times repeated. On the other hand, it is 

 interesting to observe that, out of Mr. Chadwick's three holothurians, 

 two discharged a quantity of ova before fission set in. Another interest- 

 ing fact may be gathered from Dr. Danielssen's account, to wit, that the 

 stages of growth of the new crown are similar to the ordinary stages of 

 growth in the young crinoid : the arms long remain closed, and the anus 

 is formed at a late period. Until the aHmentary canal resumes its 

 functions, whence does the rapidly-growing animal obtain its nutriment ? 

 What can be its reserve store ? Is it indebted to the dorsal organ, 

 and is this regeneration more closely allied to development ah ovo 

 than we think ; or does the animal live on the blood contained in 

 the cavities of the stem ? 



Few observations have yet been made on the relations of spon- 

 taneous fission to sexual reproduction in the Echinoderms, and the 

 subject seems to afford a fertile field for investigation, not without its 

 bearing on the deeper problems of the time. 



The Depths of the Sea. 



Increased knowledge of the depths of the sea will no doubt help 

 us to a solution of problems like those we were discussing in the fore- 

 going paragraph ; but, notwithstanding the numerous exploring 

 voyages of the past 20 years, we have still much to learn about this 

 part of our globe. 



Dr. Otto Pettersson has just published, in the Scottish Geographical 



