STRUCTURE AND DEVELOPMENTAL RATE 183 



In studying the early embryos of Fundulus these several steps 

 have actually been observed. An observation of further import- 

 ance in this connection has also been made, but unfortunately at 

 present on very few specimens. In attempting to discover the 

 earliest stages of doubleness from great numbers of eggs, I have 

 selected all specimens seeming in any way to possess two early 

 embryonic shields. On two occasions a fair number of such 

 specimens were apparently found, one lot of seven such eggs and 

 another of five. These seemingly double-embiyo formations were 

 isolated and observed during later stages, with the result that 

 from among the seven specimens only two double-headed indi- 

 viduals arose, while the remaining five formed typically single 

 embryos. The second group of five seemingly early double 

 shields gave rise to five perfectly single specimens. There would 

 appear to be only one interpretation for such a phenomenon: 

 two initial buds may sometimes appear, but later one is com- 

 pletely suppressed by the other, or the two possibly fuse com- 

 pletely and only one normally single individual is developed. 

 Therefore, it would seem that initial multiple buds are much 

 more common than the resulting double specimens indicate, and 

 that many secondary buds are suppressed or lost during early 

 development. A comparison of the two components in older 

 double monsters which is undertaken in a further section of this 

 paper makes still more probable such deductions. 



I wish to present these observations on the early double speci- 

 mens with the chances of error fully in mind. In the first place, 

 I succeeded in isolating a very few such probable earl}^ specimens, 

 twelve from the many hundred eggs examined, and from these 

 twelve only two actually showed double conditions during their 

 later stages of development. The early embryonic shields were 

 irregular and not strongly expressed. On the other hand, it 

 seems to me significant that from the twelve specimens which 

 were isolated two of them definitely developed double embryos, 

 while it is recalled that among the great numbers of Fundulus 

 eggs experimented on extremely few double specimens actually 

 occurred. However, when one selects early specimens thinking 

 them to be of a definite type and they later develop into indi- 



