ON EGGS OF MARINE ANIMALS 15 



So far as I know the only information we have concerning 

 Amphioxus is that, according to Hatscheli (1882), the eggs lose 

 capacity for development very quickly: they develop normally 

 only when shed into water in which the males have previously 

 discharged their spermatozoa. 



Polyspermy 



In general, all normally monospermic eggs that I have 

 studied, are never polyspermic if they are in optimum condition. 

 The reported polyspermy in eggs of Membranipora (Bonnevie, 

 1907) I could not during a year's study at Naples, confirm 

 (Just, 1934.) The alleged polyspermic fertilization of Pedicel- 

 Una (MacBride, 1914) is due to misunderstanding of Hatschek's 

 report (1887) that he observed spermatozoa in the perivitelline 

 space. For any of the eggs named in the foregoing, and for all 

 those specially treated in this book, polyspermy is a sign of low 

 vitality. 



Tempo of Development 



If one takes a suspension of Arhacia eggs known, by means 

 of one of the criteria discussed above, to be perfectly normal 

 and inseminates them with a freshly prepared sperm-suspension 

 and at the same time takes a suspension of Echinarachnius eggs 

 which are also perfectly normal and inseminates these, one can 

 observe the development of these two species of eggs under 

 identical conditions with respect to temperature, volume of sea- 

 water, etc. One learns that the rate of development in the 

 two species is not the same. The larger, more transparent 

 Echinarachnius egg develops more slowly. In like manner, one 

 can make a comparison between eggs of Nereis limhata insemi- 

 nated at the same instant that a Platynereis megalops lays its 

 eggs. The larger, more transparent Platynereis eg^ reaches first 

 cleavage before the egg of Nereis. If one goes farther afield 

 and compares eggs of distantly related species one notes again 

 that under uniform conditions the tempo of development varies 

 with different eggs. It is apparently not possible to correlate 

 these differences with any visible characteristic, as size or 

 transparency of the eggs. The problem of the tempo of develop- 

 ment is one worthy of more attention than it has received. 



