OCTOBEE 2, 1908] 



SCIENCE 



455 



condition and the other in a plus condition 

 the condition of the organ in the children will 

 depend upon the germ cells (and hence on the 

 parents) of the advanced parent. If half of 

 its germ cells are in the minus condition, as 

 may he the case, half of the children will have 

 the organ in question in the minus condition. 

 Even if both parents are in an advanced condi- 

 tion, if they both have the less advanced condi- 

 tion recessive, one quarter of their offspring 

 will have the organ in a minus condition. 



The foregoing principles help us to under- 

 stand the reason for the degeneration that 

 sometimes, but not always, follows inbreeding. 

 If the children can not rise above the level of 

 their parents but may fall below in respect to 

 any organ, it is plain that if brothers and 

 sisters were to mate the average of the off- 

 spring would rapidly run down hill to the zero 

 condition of the organ. In the mating of 

 cousins the same result would tend to occur, 

 but not so rapidly and certainly. The more 

 foreign blood introduced the less the danger 

 of degeneration. 



Another class of degeneration is illustrated 

 by albinism. Studies that Mrs. Davenport 

 and I have been making show that there are 

 in human hair two pigments, black and red, 

 occurring in various dilutions and combina- 

 tions, as will be more fully set forth in our 

 paper on human hair color to appear shortly 

 in the American Naturalist. There are, how- 

 ever, cases of black (N) hair with no red (r) 

 pigment, and of yellow or red (R) hair with- 

 out black pigment (n). The gametic formula 

 of the former is Nr and of the latter nR. 

 The grandchildren of Nr and nR consorts will 

 have hair of either of four kinds : black-and- 

 red (NR, chestnut, or mahogany colored), jet 

 black iNr"), clear yellow or red {nR"), and 

 colorless (nr) ; the latter are albinos. 

 Studies that I have been making on albinos 

 reveal an ancestry in conformity with this 

 hypothesis. We see, then, that albinism is not 

 a sport occurring in wholly arbitrary fashion; 

 but a necessary, predictable result of certain 

 combinations of gametes. The only part that 

 inbreeding plays is to make more probable the 

 necessary combination of gametes. The de- 

 generation in this case follows from the union 



of two negative factors in dihybrids ; and this 

 is a cormnon cause of degeneration. 



Chas. B. Davenport 



the question of cyclopia, one-eyed monsters 



Two summers ago I found it possible to 

 produce one-eyed fish embryos by means of 

 MgClj solutions in sea water.' At that time 

 the spawning season of the fish used, Fundulus 

 7( ( teroclitus, was nearing a close, so that it 

 was impossible to obtain material showing the 

 early conditions of the defect or to rear the 

 embryos in order to observe their actions after 

 hatching. 



During the present summer more extensive 

 experiments have confirmed the fact that 

 Cyclopean embryos may be produced in any 

 number desired by treating the eggs with 

 MgCl, or M:g(]SrO,), solutions. The effect 

 seems due to the Mg ion in the presence of 

 certain sea-water salts. The embryos may be 

 hatched and the cyclopean eye seems func- 

 tional, many of the fish swimming in a normal 

 fashion and responding to light. These free- 

 living Cyclopean fish may be kept for as long 

 a period as the normal swimming embryos, a 

 period of eight or ten days, after hatching, at 

 which time all die of starvation, since the 

 entire content of the yolk-sac has been ab- 

 sorbed and no other food is furnished. The 

 Cyclopean individuals could doubtless be reared 

 if their proper food was known. 



A study of these cyclopean embryos from 

 the first appearance of the optic vesicles to 

 hatching, both in life and sections, has proved 

 that the earliest indication of an eye is just 

 as truly cyclopean as it will be later. All de- 

 grees from a perfectly single organ through 

 various conditions of doubleness to two inti- 

 mately approximated optic cups may be found 

 in young embryos. My former statement that 

 the cyclopean eye resulted from a fusion of 

 the elements of the two eyes after their 

 formation, a statement based on comparisons 

 of cyclopean eyes in late stages of develop- 

 ment, is incorrect, as is also a similar idea 

 advanced by Dr. Mall in his recent paper.^ 



' Stockard, ArcMv fur Entw.-Mech., XXIII., 

 1907. 



= Mall, Jour. Morphology, XIX., 1908. 



