136 Papers from the Marine Biological Laboratory at Tortugas. 



the normal and the hybrid was so striking that it needed no confirmation 

 by other observers, but purely as a matter of personal interest I asked four 

 other investigators at the laboratory to look at the two sets of living larvae 

 and describe their observations to me. The independent observation of 

 each of these investigators was a confirmation of my own. 



The succeeding stages show considerable variation. In some the 

 growth of the archenteron ceases and the blastocoele becomes filled with a 

 mass of opaque cells (fig. 11). In others gastrulation continues. In a few 



Fig. 1 1 . — Optical section of Toxopneustes cf xCidaris 9 

 abnormal gastrula; blastocoele nearly filled with 

 opaque cells. 40 hours. 



cases a small skeletal spicule was formed in the mass of mesenchyme cells 

 at the base of the archenteron. I was unable to keep the hybrid material 

 alive beyond the gastrula stage. 



GENERAL DISCUSSION. 



We have already noted Boveri's conclusions regarding the early influence 

 of the sperm on development. My results confirm his general thesis as 

 to an earlier influence than that commonly accepted, although my con- 

 clusion is based on evidence not afforded by his crosses. 



In the nature of the case the results given by inseminations in which the 

 sperm nucleus does not unite with the egg nucleus are without direct value 

 in this connection. They may have an indirect value in showing that the 

 sperm cytoplasm, if it has become a part of the egg cytoplasm, has not 

 influenced the early development. As has already been indicated, the 

 larvae obtained from such inseminations are essentially parthenogenetic. 



The only investigation of which I know, which is closely comparable 

 to mine, is that of Godlewski (1907), and even here we are comparing the 

 reciprocal cross between forms whose early development is similar. In 

 Godlewski's cross the fertilization of echinoid eggs (primary mesenchyme 



