ON thp: experimental hybridization of echinoids. 



Expressed in tabular form, these results are as follows : — 



305 



10. Inheritance of the Late Larval Characters in 1912. 



The inheritance of the late larval characters in 1912 was not the same as in the 

 previous years, and for that reason is treated in a separate section. A change in 

 inheritance, such as is described below, is very surprising, and the question naturally 

 arises, as to whether it was an actual change, or was due to some change in the 

 methods employed in the experiments. This cannot, however, possibly have been the 

 reason for the difference found, for exactly the same technique was adopted in 1912 

 as in the previous years. Moreover, the results given are founded, not on a few 

 experiments, but on a large number which were carried on from the end of February 

 until September. When the plutei had become fully developed, each one was 

 examined separately. 



The following account applies to the inheritance of the two definite characters 

 which have been investigated before, that is to say, the presence or absence of 

 the posterior ciliated epaulettes and the presence or absence of the green pigment 

 masses. It is important to mention here that the pure-bred plutei developed 

 these characters in the same invariable way that they had done in former years. 



Crosses between E. esculentus and E. miliaris. 

 1. E. esculentus^ X E- miliaris $ — 



With one exception, all the cultures of this cross gave larote with matertial characters, 

 as in iirevious years. The hybrids were of the form of E. esculentus, and had 

 posterior ciliated epaulettes and a complete absence of green pigment (Plate 22, fig. 73). 



The exception mentioned was one cross which gave larvae of which the following is 

 a description. The plutei had the general shape of E. miliaris, with a broad body, 

 domed aboral end, and short arms. There was, however, no trace of the green 

 pigment, so that the inheritance of this character was, as usual, maternal. There 

 were very few larvfe in the only culture of this cross which survived, but they 

 were healthy. The point in which this experiment difiered from the others was 



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