258 MESSES. C. SHEARER, W. DE MORGAN, AND H. M. FUCHS 



urchins. We wish to thank him for this and for the trouble he has taken in 

 identifying material we have sent him at various times. The results of his 

 examination of the hybrid urchins are published in Section 1 5 of this paper. His 

 report on material will be found under Section 3. 



The work has been carried on at the laboratory of tlie Marine Biological Associa- 

 tion at Plymouth, and we have to thank the Director and his staff for their constant 

 attention to our requirements, wliich have entailed an undue amount of labour on the 

 collecting department of the Station. Material of E. esculentus and E. acuLus at 

 Plymouth is only obtainable some miles from land, l)y trawling in deep water. These 

 forms, however, can be obtained in greater quantity than E. miliaris, which can only 

 be collected in rock-pools at lowest spring tides. To the Director, Dr. Allen, we 

 feel specially indebted for constant advice and encouragement. 



2. Literature. 



BovERi(9) was the first to investigate the hybrids between different species of 

 Echinoids. As a preliminary to the fertilization of enucleated portions of Sphmrechinus 

 eggs with Echinus sperm, he investigated the ordinary inheritance in this cross, and 

 found the hybrids to be of an intermediate form between the two parents. He then 

 broke up some of the eggs by shaking and, without isolating the fragmented eggs, he 

 fertilized with Echinus sperm. The resulting larvae were of three types : ordinary 

 sized larvfe of intermediate type, dwarf larvae of intermediate type, and dwarf larvae 

 of purely paternal type. The latter he considered to have been derived from the 

 enucleate portions of SphvBrechimis eggs, thus proving the nucleus to be the carrier of 

 hereditary characters. 



In 1894 Seeliger (78) crossed SphcBrechinns $ X Echinus $ at Trieste, and found 

 that all the hybrids were not of intermediate type, as stated by Boveri, but that a 

 certain number of purely paternal larvae were present in every culture. This 

 conclusion cast doubt on BovERi's results. 



In 1895 Morgan (65-67) got the same result as Seeliger, with this cross, at 

 Naples. Now Echiyius microtuherculatus has a single rod as the skeletal support of 

 the postoral arm, while Sphcerechinus granularis has a lattice skeleton. The number 

 of prongs in the skeleton of this arm was used as the chief index in determining 

 which parent the hybrid most resembled, but Morgan pointed out that the hybrid 

 skeleton is very variable, especially in the number of these rods, and he went so far as 

 to say that no certain conclusion could be based on the shape of the skeleton in 

 general. 



In 1895 Boveri (10) replied to Seeliger and Morgan. He repeated his hybridiza- 

 tion experiments, investigating in the larvje especially the form, the number of rods 

 in the postoral arms, and the presence or absence of a " Scheitelast " to the antero- 

 lateral arm. His former contentions remained unchanged, and he attempted to 

 explain Seeliger's results by suggesting that at Trieste the larvae of the parental 



