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



were placed respectivelv in the normal, alkaline, or acid waters. The work reads as 

 if ditfereiit parents were used. If this should be the case, then no accurate 

 comparisons can be made. If, however, tlie same parents were used, the tables 

 certainly show an increase of Toxopneastes iuliuence in acid water, as Texnent 

 maintains. 



The figures given of the larvfe are by no means clear, and it is difficult to say 

 whether or not tliey bear out the statement of the text.* They show a certain 

 number of stunted and malformed larvaj, but certainly many of the hybrids are well 

 developed and healthy. 



In 1911 we published (79) a preliminary paper giving the results of our work 

 up to date. 



In lull MacBride (57 and 58) made the cross Echinocaniiuvi cor datum '^ X 

 Echinus esculentus $ at Millport, Scotland, in order to trace the inheritance of the 

 aboral process of the Echinocard ium larva, a feature quite absent in Echiniix. 

 A small proportion of the eggs fertilized, and these grew very slowly and gave rise to 

 unhealthy and for the most part deformed larvje, few living longer than eight days. 

 One alone developed the maternal apical spike. The majority, however, did not live 

 more than five or six days, and did not develop the spike. MacBride considers the 

 absence of the spike a paternal character, but as he did not obtain the reciprocal 

 cross the evidence on which he ba.sed this conclusion is indecisive. 



In 1912 FucHS (28) hybridized the same species at Plymouth, but obtained both 

 reciprocals of the cross. Of these E. esc'dentus ? X Echmocarditim cordatum $ was, 

 contrary to MAcBRiuii's experience, most readily obtained, and proved the least 

 unhealthy. FlTCHS points out that the wide difference separating these species is 

 such as to render the resulting larvae derived from crossing them invariably 

 pathological. This is borne out by the fact that very few survive more than seven 

 or eight days, and always die after becoming highly abnormal and stunted. It is 

 doubtful, therefoi-e, if soiuid deductions can be drawn from the hybridization of these 

 forms. In the cross ^c/im».v $ X Echinocardium $ all the larvae inherit the absence 

 of the aboral process from the female parent. In the reciprocal the majority are 

 highly abnormal, and have the paternal absence of the aboral process ; but among 

 these there are always a few more healthy than the rest, and these develop the 

 maternal aboral process. When the paternal character dominates it would seem to 

 produce exceptionally unhealthy larvae. 



In view of the very unhealthy larvae obtained by both MacBride and FucHS in 

 hybridizing Eclnnocardmm and Echinus, it is obvious that the specific difierences 



* The figures are somewhat confused, and 19 are described difforentl}' in the text and in 

 the description of the plates. For instance, figs. 66-69 are described in the text as derived from 

 acid-water cultures, while in the description of the plates they are said to be derived from ordinary 

 water. Fig. 86 in the text is stated to be from an acid-water culture, while in the description of the 

 plates it is put down as from a XaOH culture. 



