ZOOLOGY AND BOTANY, MICROSCOPY, ETC, 205 



Of great importance is the inquiry into the influence which the 

 primary organs exert on each other's further development. Herbst 

 found that if the eye-stalk of a shrimp is amputated, the animal grows a 

 new one ; if the optic ganglion be also removed an antenna-like organ 

 is formed. This must be due to the presence or absence of some 

 chemical substances, like hormones. Lewis found that if the optic 

 vesicle of a tadpole's brain was cut off and pushed into a new position 

 beneath the skin, a lens developed from the skin at the new spot. 

 There must be emanations from the optic vesicle. It is possible, as 

 J. T. Cunningham has suggested, that specific hormones or the like may 

 be liberated from modifications of tissue, and may pass to the germ-cells. 



Twin-embryos in Duck.* — Edward S. Ruth describes four sets of 

 twin-embryos of the duck. Twins may be divided into (1) dissimilar, 

 (2) identical, and (3) joined twins. The first type results from the 

 fertilization of several ova, or possibly a multinucleate ovum ; the 

 second type arises from the separation of early blastomeres or parts of 

 one ovum ; the third type includes all those twins that are joined — 

 probably due to an incomplete separation of the early blastomeres, or of 

 the embryo-forming substance at some later stage. The identical and 

 joined twins belong to the same category. In the four sets of duck 

 twins, three sets were joined, while in the remaining one the twins were 

 separate. 



Siamese Grafting. f — 0. Laurent calls attention to the possibility of 

 making a vital union, which he terms " Siamese grafting," between two 

 higher animals. He has succeeded with fowls and with ducks. More 

 remarkable was a junction effected between fowl and pigeon, and 

 another between pheasant and duck. He has applied the idea twice to 

 wounded soldiers, and thinks it may have a future of importance. 



Inheritance in Guinea-pigs and Rats.| — W. E. Castle obtained in 

 Peru a wild species of guinea-pig, the probable ancestor of the domesti- 

 cated forms, identified as Gavia cutler i Bennett. He also procured a 

 feral race from lea, and domesticated Peruvian guinea-pigs. It can be 

 stated, with probable correctness, that the guinea-pig has undergone^ in 

 domestication, more extensive variation in colour and coat characters 

 than any other mammal, and that this variation has occurred almost if 

 not quite exclusively under the tutelage of the natives of Peru. This 

 conclusion points either to a great antiquity of the guinea-pig as a 

 domesticated animal or to more rapid evolution by unit character 

 variation than by other natural processes. It may be noted that the 

 Argentine G. aperea has perhaps given origin to some domesticated 

 races, and that when the Brazilian G. rufescens is crossed with the 

 domesticated guinea-pig only the female progeny are fertile. 



The hybrids produced by crossing G. cutleri with the domesticated 

 guinea-pig are all fertile, and the results show that the colour varieties 



* Philippine Journ. Sci., xi. (1916) pp. 110-17 (3 pis.). 



t Comptes Rendus, clxiv. (1917) pp. 62-3. 



X Carnegie Inst. Washington Publications, No. 241, pp. 1-192 (7 pis.). 



