IV. i INITIAL STRUCTURE OF THE GERM 



261 



An explanation of the discrepancies in the results of the different 

 observers has been offered by Vernon. Vernon has found that 

 Strongylocentrotiis lividus (which has a Pluteus almost exactly like 

 that of Echinus) is at a minimum of sexual maturity in the summer 

 months, but that from that time onwards the power of the male to 

 transmit its characters to the hybrid larva, when crossed with 

 Sphaerechimis ? , increases, and that it is 

 possible to obtain a culture consisting en- 

 tirely of larvae of the paternal type, in 

 respect, that is to say, of the skeleton. 

 Vernon was inclined to look upon this 

 difference in maturity as a seasonal varia- 

 tion, but Doncaster has since attributed it 

 to the effect of temperature alone. 



The transmission of the characters of the 

 skeleton may therefore be the function of 

 the nucleus, though, as just pointed out, 

 there is no stringent proof of this. There are 

 other larval characters, however, which, 

 as Driesch has justly urged, must depend 

 on the cytoplasm of the ovum, the colour, 

 for example, if the egg is pigmented, and 

 the size of the larva, so far as this depends 

 on the size of the egg. From a series 

 of hybridization experiments between 

 Echinus, Sphaerechinus, Strongylocentrotus } 



and Arlacia, Driesch indeed concludes 



j_r 4. ji , P n j- A At &, Young dwarf larva of 



that the rate of cell-division up to the tho pur s e Echinus type 



formation of the primary mesenchyme, reared from an enu- 

 the vacuolation of the ectoderm cells (in ^ f eat | ^aeS^ius^fe^- 

 Sphaerechinus), the number of the primary tilized with the sperm 



mesenchyme cells, are all characters which ?f ^QQC^ ( After 

 > Boveri, 1896.) 



depend on the ovum, and the ovum alone, 



and therefore on its cytoplasm. With regard to the skeleton 

 Driesch admits that this, and hence, indirectly, the shape of the 

 larva, may be influenced by the sperm, at least when the egg 

 of Sphaerechinus is fertilized either by Echinus or Strongylo- 

 centrotus. Fischel has made similar experiments and arrived 

 at a like conclusion. 



Fm. 159.- , Fully 

 formed Pluteus of Echi- 

 nus microtuberculatus. 



