314 MESSRS. C. SHEARER, W. DE MORGAN, AND H. M. F0CHS 



masses were invariably inherited through the maternal parent. Tennent, on the 

 other hand, made his experiments with forms of which one dominated over the other, 

 irrespectively of which way the cross was made. Thus it will be seen that at 

 Plymouth we started from a different basis from that on which Tennent made his 

 investigation. As the result of our experiments, of which an account is given 

 below, it was found that a change in the OH-ion concentration of the water in which 

 the fertilizations were made had no effect at all on the inheritance. Nevertheless 

 this cannot in any way be said to disprove Tennent's work, since he was dealing 

 with a different type of inheritance. What it means is, that such a change in the 

 external medium lias no effect on the transmission of characters in hybrids between 

 the species of Echinus at Plymouth. 



These experiments were made Avith the reciprocal crosses between E. esculentua 

 and E. miliaris and between E. acutu^ and E. miliaris. The alterations in the 

 OH-ion concentration of the sea-water were made by the addition of definite 

 quantities of standard solutions of sodium hydrate and of hydi'ochloric and acetic 

 acids. Fertilization was brought about in the usual way in these solutions, and the 

 eggs remainded in them during the segmentation period. When the blastulae swam 

 to the surface some were transferred to jars ofnoiunal sea-water, others to jars of sea- 

 water of the same OH-ion concentration as that in which the fertilization had been 

 made. It was found, however, that in all cases when larvae were reared in water 

 other than normal, they gradually died off, only a few unhealthy individuals ever 

 reaching a late stage. In consequence this method was discontinued, all the 

 observations being made on cultures of plutei which had been transferred to ordinary 

 sea- water at the blastula stage. 



Experiments were made to determine the maximum amounts of acid and of alkali 

 which could be added to the water without injuring the eggs. It was found that 

 although in some cases as much as 1 c.c. N/10 NaOH or HCl or acetic acid per 

 200 c.c. sea-water could be used, yet when the larvte reached a late stage they were 

 almost all malformed. In order to get numbers of healthy larvse at a late stage, the 

 maximum amounts that could be used were 0'5 c.c. N/10 NaOH or HCl or acetic 

 acid per 200 c.c. sea-water. 



The eggs from each female were divided into four portions. One was placed in 

 the alkaline water, one in the acid water, and a third in ordinary sea-water. Each 

 was then fertilized with sperm from the same male. The fourth portion was kept as 

 an unfertilized control. 



When the larvse had reached the four-armed stage a large number were examined 

 in each experiment. It was found, however, that there had been no change in the 

 inheritance of the skeletal characters. 



Again, when the plutei had become fully formed a thorough examination was made 

 to see whether there had been any alteration in the inheritance of the posterior 

 ciliated epaulettes or of the green pigment masses. It was found that in no case did 



