ON THE EXPEEIMENTAL HYBRIDIZATION OF ECHINOIDS. 



265 



separating these forms are far too great to allow of their ever producing anything but 

 highly abnormal larvae. Hybrids of this nature are of little value in the investigation 

 of general problems of heredity, and investigators will do well to avoid their study in 

 future. 



In 1912 Debaisieux (16) repeated our work of 1911 on E. acutus, E. miliaris, 

 and E. escvlentus, adopting the same criteria of inheritance, namely, the ciliated 

 epaulettes, pedicellarise, green pigment, etc. The work was done on material 

 collected at Plymouth and sent to the Imperial College, London. His results agree 

 in every respect with our own for 1912. We have in addition found a few 

 variations, especially with regard to the cross E. eaculenhis % xE. miliaris $ , not 

 found by him, and probably due to our observations being based on a much greater 

 amount of material and larger number of cultures. Our results are compared in 

 tabular form below. 



3. — Material. 



The following is a list of the localities near Plymouth at which it is possible to 

 collect the species of Echinus on which we have conducted our experiments : — 



Echinus esculentus and E. acutus equally common : — 



1. Looe-Eddystone grounds. 25-30 fathoms. In the region about 6-8 miles 



E. of Kame Head and about 7 miles N.N.W. of the Eddystone Light- 

 house. Nature of bottom — Fine sand and patches of coarse gravel. 



2. Inner Rame, Eddystone grounds. E. esculentus common, E. acutus rather 



scarce. 24-28 fathoms in the region 4-5 miles S. of the Breakwater in a 

 direction roughly E. and W. Nature of bottom — Fine sand. 



3. Outer Rame, Eddystone grounds. E. esculentus fairly common, E. acutus 



occasional. 28-30 fathoms; 3-4 miles N.N.E. of the Eddystone Light- 

 house, thence up and down Channel E. and W. for 2-4 miles. 



4. Outer Mewstone trawling ground. 25-27 fathoms. E. esculentus fairly 



common, E. acutus relatively scarce. 5-6 miles S. of the Mewstone. 

 Trawling is sometimes done farther out in deeper water down to 

 30 fathoms. Nature of bottom — Finest sand. 



VOL. CCIV. — B. 2 M 



