126 CRESSWELL SHEARER, WALTER DE MORGAN, H. M. FUCHS. 



abnormal or unhealthy Plutei. No drawings or observations have 

 been made of any such larvae, and all crosses showing an unusually 

 large percentage of abnormalities have been thrown away and the 

 experiments repeated. It is remarkable, however, how frequently 

 abnormalities, especially with regard to the development of the arms 

 and skeleton, are to be seen in Plutei taken from the Plankton. 



Although we have had no difficulty in rearing Plutei in considerable 

 numbers through metamorphosis, and some of our young hybrid 

 urchins are now, after two years, one centimetre in diameter,* we have 

 not succeeded so far in bringing them to a stage of sexual maturity. 

 This is doubtless due to the fact that we have been unable to furnish 

 them with the proper food. For it would seem, from what we have 

 been able to discover regarding E. miliaris, that individuals of this 

 species at least can become sexually mature within the first year of 

 their existence, in a state of nature, and can attain the size of some 

 six centimetres. As none of the E. miliaris hybrids in our cultures 

 in the laboratory have shown any such rapid rate of growth, we feel 

 that we have only partially succeeded in our feeding methods. 



During the first few weeks after metamorphosis the young Echini 

 thrive readily on the "red weed" {Delcsseria), but after this they soon 

 cease to grow, and evidently at this stage a further change of food is 

 necessary. What exactly this change should be we have so far been 

 unable to find out, and we have simply allowed them to remain in 

 culture jars in the hope that they will find their proper food among 

 the algae growing there. 



It is the ultimate object of our work to bring the hybrid urchins to 

 sexual maturity and, if possible, investigate the characters of the 

 second generation. Our experiments of the last three years seem to 

 point to the improbability of accomplishing this under laboratory 

 conditions, and we are at present devising a method for confining our 

 young hybrid urchins on the sea bottom in their natural habitat. 



It is obvious, however, that all laboratory conditions differ in many 

 essentials from those obtaining in nature. For this reason we have, 

 this year, raised Plutei from the first in the sea, by confining them 

 in jars in the chambers of a floating box, which is anchored some 

 miles out, in the clearer water of Plymouth Sound. We have 

 not noticed that our Plutei reared under these conditions grow more 

 rapidly than those kept in the Laboratory, and this would seem to be 

 due to the lack of food. It seems to be impossible to get any pro- 

 tected water where the Plutei might be confined, as rich in the Diatom 



* One hybrid, raised at Cambridge, is now 3 cm, in diameter. For figures of same, 

 vide Nature, Vol. LXXXVII, p. Ill, 1911. 



