ON THE BREEDING HABITS OF ECHINUS MILIARIS. 255 



there is a distinct instinct for association of individuals at the time of 

 sexual maturity, and that the association frequently, but not always, 

 results in pairing of the sexes. In this respect the position in which two 

 of the above pairs of male and female were taken is specially interesting. 

 Both pairs were situated under a large stone whose lower surface was 

 somewhat rectangular, and would measure rather more than two feet 

 on the longer axis. The pairs were on the opposite ends of the lower 

 surface near the edge of the stone on the long axis, and each member of 

 a pair was closely opposed to the other. It would thus appear that these 

 four urchins had definitely mated in pairs. 



Of the 57 remaining groups taken, 41 contained all ripe individuals, 

 and combining these 41 groups with those given above, it was found 

 that out of the total of 66 associations of ripe specimens, 41 were (J $, 

 9 of various sexes, 8 $ $, 6 <:^ c^, and 2 ? $ $. Thus in all the groups of 

 ripe forms there were 40 pairs of opposite sexes and 8+6+2 = 16 groups 

 exclusively of one sex or the other. Therefore, leaving out the 9 groups 

 containing various sexes, it is seen that the number of pairs, namely 41, 

 is greater than twice the number of the groups which contain one sex 

 or the other. Consequently it is highly probable that the statement 

 that the sexes of E. miliaris associate definitely for the purpose of breeding 

 is significant. 



In the whole of the groups collected, regardless of ripeness of the 

 gonad in all the members of the group, there were 47 pairs of (^ and $, 

 15 pairs $ $, Q ^ S, 8 groups of more than two containing both sexes, 

 2 groups ? ? ?, 1 S S Sj 3,nd 5 containing one or more immature forms. 

 In the groups recorded as not all ripe there were some specimens quite 

 ripe. Many of the other urchins in these groups, however, would probably 

 have yielded some embryos if their sex cells had been mixed with those 

 from similar forms of the opposite sex, but an attempt based on experi- 

 ence was made to name those forms ripe which would probably have 

 yielded a good proportion of segmenting eggs as a result of fertilization. 

 In this branch of the investigation I am indebted to Mr. H. M. Fuchs 

 for some help in determining the state of the gonad. 



A more significant result could doubtless be obtained by an examina- 

 tion of a larger number of pairs of E. miliaris obtained about the same 

 time and during the breeding season, but the opportunities for such an 

 investigation are not very common. E. miliaris can often be taken in 

 numbers by dredging, and then I have frequently observed that many 

 individuals are taken matted together, and in such a way as to suggest 

 they were actually in that condition before being captured by the dredge. 



