ON THE EXPERIMENTAL HYBRIDIZATION OF ECHINOIDS. 261 



regard to the number of primary mesenchyme cells. He stated that double- 

 fertilized eggs had an unecjual amount of mesenchyme in the two halves of the 

 larvae, and that the mesenchyme was therefore influenced by the sperm. He found 

 that the sperm aflected also the form, size, and pigmentation of the larvpe. 



In this controversy between Boveri andDRiKSCH it is very difficult to decide which 

 was in the right, as tlie criteria used to determine the dominance were so questionable. 

 Driesch, for example, suggested that BovERl used unhealthy larvas in which to 

 count the mesenchyme cells, or that he counted in other cells with them. 



Peter (73) attributed these conflicting results to the great individual variation 

 which he found in the number of mesenchyme cells within each species Again, 

 the form of the larvae is a very doubtful point on which to decide the inheritance. 

 Driesch stated that the shape of the larvae was maternal, except when influenced by 

 the skeleton ; but Boveri claimed to have found paternal influence in the shape of 

 very young larvae, before the development of the skeleton. He admits that the 

 shape may be maternal, but Driesch states that it is always so. 



lu 1906, FiscHEL (27), working at Villefranche, crossed Arhacia jmstulosa, Echinw^ 

 hr-evispinosus and Sti oiigyloceidroUis lividus. In opposition to Driesch, he concluded 

 that tlie hybrids were not purely maternal, but that the sperm had, in many cases, an 

 influence on tlie form, size, pigment, and skeleton. He regretted, liowever, that he 

 was unable to rear the larvae long enough to study the later stages. In discussing 

 the capriciousness of crossing, he stated that when a cross is going to succeed 

 many spermatozoa collect in a broad zone round each Qgg, but that when it is 

 not going to develop few gather. This has not been our experience. We have 

 found that, in many cases, when a cross is not going to be successful the eggs 

 will be surrounded by a sphere of sperm. 



In 1906, Herbst (39) made an elaborate study of the action of temperature in 

 influencing inheritance in the hybrids derived from crossing Sphcerechinus eggs 

 with Strongylocentrotiis and Echinus sperm. He found that an increase of 

 temperature gave multiple rods and incipient lattice formation in Echinus. 



He was also of opinion that there is also a factor independent of temperature, 

 which determines in a lesser or greater degree the predominance of paternal or 

 maternal characters, and this he thought was to be found in the varying nature 

 of the egg substance itself. 



It wiU be remarked that both Doncaster and Herbst studied the action of 

 temperature after fertilization. Our own experiments would seem to show that 

 once fertilization has t;iken place little change can be brought about in the type 

 of inheritance, and that it is to the growing period that we should turn for the 

 action of temperature on the germ cells. 



Herbst reached the same conclusion as Doncaster with regard to the effect of 

 deterioration of the sexual products on the transmission of characters. He injured 

 the germ cells by eliminating the magnesium from his sea-water, and by diluting 



