574 E. W. MAOBRIDE. 



contended tliat the mere act of cutting out the ovary is 

 competent to produce such an eifect. This is negatived by 

 the fact tliat in one culture raised from artificial fertilisation 

 some larvae were found showing a well-developed vacuolated 

 crest. The much more probable assumption is that abnormal 

 development results from the fertilisation of eggs wliich are 

 not quite ripe. 



Up till now development following on fertilisation has been 

 taken as adequate proof of the ripeness of an egg, as anyone 

 who reads the numerous papers of Driescli, Herbst, Loeb^ and 

 other workers on what is called " Developmental Mechanics " 

 may readily see. But when working with Echinus escu- 

 lent us I obtained some evidence that this is not necessaiily 

 the case. I was^ however, so much astonished by the facts 

 which came to light that I have not until now dared to 

 publish them, and only do so now that a similar state of 

 affairs has been discovered with reference to the development 

 of Ophiothrix fragilis. I found that in order to obtain 

 good cultures of the larvae of Echinus esculentus it was 

 necessary to choose for artificial fertilisation specimens which 

 were thoroughly ripe. This thorough ripeness was evidenced 

 by the condition of the ovary. When this organ at a touch 

 dissolved into eggs, then the resulting culture was higlily 

 successful. When, however, I tried to fertilise eggs from 

 half-grown specimens, I obtained indeed some larvje, but 

 these were small and had imperfectly developed arms, and 

 lived only a few days. 



Of course, as all know, an egg is incapable of fertilisation 

 until it has formed its two polar bodies, but this process, in 

 some animals at least, is hurried on by the mere presence of 

 the spermatozoa. In the American oyster it is impossible by 

 inspection under the microscope to discriminate between ripe 

 and unripe eggs, for in this species the membrane of the 

 nucleus of the oocyte remains undissolved until it comes into 

 contact with the spermatozoa. It seems, therefore, allowable 

 to conclude that although in Echinoderms polar bodies are 

 normally formed independently of the presence of sperma- 



