344 MESSRS. C. SHEARER, W. DE MORGAN, AND H. M. FUCHS 



laws, at other times all the ottspring were maternal. When more distinctly related 

 species, such as T. horteyisis and T. mistriaca, or T. nemorcdis and T. austriaca, were 

 hybridized, only maternal offspring resulted. Lang suggests that when purely 

 maternal offspring — or " false hybrids," as he calls them — result, there has been no 

 true fertilization. In any case it is important that when crossing the same forms he 

 got on some occasions one type of hei-edity, on others another. 



D. T. Macdougal (59) found different behaviour In (Enotlie7-as crossed at New 

 York from those crossed by De Vriks in Holland, although using, as far as coiild be 

 determined, identical material. He says : " Aiauy indications lead to the suggestion 

 that the dominancy and prevalency, latency and recessivity of any character may 

 be more or less influenced by the conditions attendant upon the hybridization, the 

 operative factors might include individual qualities as well as external conditions." 



We have emphasised in the foregoing sections how previous investigators have 

 used characters that have not been definite eno\igh to give a final answer to their 

 investigations in Echinoderm hybridization. Nevertheless, the frequent inconsistencies 

 between the conclusions of these experimenters may possibly be of a similar natui'e 

 to the change of inheritance we experienced in 1912. 



BovERi (y), working at Naples, found the hybrids of the cross Sphcerechinus $ 

 X Echinus $ were intermediate in their characters between both parents. 

 Sekliger (78) repeated this cross at Trieste, but found that in every culture some 

 of the larvae were purely paternal. 



Morgan (65) repeated this work at Naples, and substantiated Seeliger's 

 conclusions. In this case too, then, there would seem to have been a change in the 

 character of the inheritance of the skeleton at Naples. 



This was in regai'd to the inheritance of the larval skeleton. In Sphwrechinu^ the 

 skeleton is of the multiple-rod or lattice type, while in Echinus it is a single rod ; 

 but in Echinus the multiple-rod or lattice form sometimes appears in the pure-bred 

 larvge when these become unhealthy. Neither BovERi nor Seeliger appear to have 

 adopted precautions for keeping their cultures of larvge healthy. This consists in 

 having the water in which they are living free from an undue growth of bacteria and 

 infusoria, and in supplying them with their proper food. It is possible, therefore, 

 that these results are faulty. 



Similarly, the opposite results obtained in two consecutive years by Hagedoorn (.38) 

 and LoEB, King, and Moore (54), working at Pacific Grove, Cal., may both be 

 correct. Our results at least emphasize the fact that it is necessary to repeat the 

 same experiments many times, and to extend them over a considerable number of 

 years, before a correct opinion in some cases can be formed. If our investigations at 

 Plymouth had been confined to the summer of 1912 alone, we should have arrived 

 at the same conclusion as LoEB, King, and Moore (54), that certain characters are 

 definitely dominant, namely, the posterior ciliated epaulettes and posterior 

 pedicellaria3, while the green pigment is recessive. 



