504 Chronicles of Science. [J^y, 



normally, or sometimes one of them is imperfectly developed and 

 forms an acephalous monster. In other cases, the two embryos unite 

 directly and produce a double monster. These two modes of coexist- 

 ence of two embryos upon a single vitellus evidently arise from the 

 fact that in the first case the egg contains two distinct cicatriculae be- 

 fore incubation ; in the second, only one. A double monstrosity, 

 therefore, is not, as was supposed, the result of the fusion of two em- 

 bryos developed upon distinct vitelli ; and M. Dareste maintains that 

 for the formation of a double monster, the embryos must actually ori- 

 ginate upon a single transparent area, that is, in a blastoderm pro- 

 ceeding from a single cicatricula. But it remains to be seen why in 

 some cases the two embryos are separately developed, and in others 

 they form a double monster. Another important question arises, — is 

 this single cicatricula, which gives origin sometimes to two distinct 

 embryos, and sometimes to two united ones, really simple, and similar 

 to the ordinary cicatricula ; or is it the result of the early fusion of 

 two primarily distinct germs ? Since M. Balbiani has shown how the 

 germ is formed in the ovule, we may consider whether certain ovules 

 may not contain a cicatricula apparently simple, but formed by the 

 fusion of two originally distinct germs. And the coexistence of two 

 germs within a single ovule is proved by the coexistence of two sepa- 

 rate cicatriculae upon the same vitellus. 



Professor Owen has communicated to the Royal Society an account 

 of the female Echidna (Echidna hystrix) with a young one, received 

 from Dr. Miiller, of the Botanic Gardens, Melbourne, in 1865. The 

 young adhered to its mother as was supposed by a nipple. In the 

 parent, Professor Owen found two marsupial pouches, about H inch 

 apart, each with the aperture longitudinal, half-an-inch in depth, and 

 two-thirds of an inch in length. The young Echidna, about one inch 

 in length in a straight line, could be received in a bent position into 

 the pouch, and might cling to the fine hairs of that part by its claws ; 

 but there was no trace of a nipple. Each mammary gland terminates 

 by numerous ducts upon the fundus of the corresponding pouch. The 

 author concludes, from the appearance of the uterus and appendages, 

 that this Echidna had produced two young, of which only one was se- 

 cured, and that probably she had a mammary foetus in each pouch at 

 the time of capture. The young resembled tbe young of ornithorhyn- 

 chus in general shape and curvature of the body, and also the new- 

 born young of the kangaroo in the proportions of the limbs to the 

 body, in the inferior size of the hind pair, and in the feeble indication 

 of eyes and eyelids. The traces of ears, however, are less, the conch 

 being little, if at all, developed in the mature Echidna. The form of 

 the mouth is a transverse slit, and is a good monotrematous character 

 of the young at that period, since in all true or teated marsupials, the 

 mouth of the mammary foetus has a peculiar circular and tubular 

 shape. A scarcely visible linear cicatrix at the middle of the lower 

 part of the abdomen is the sole trace of umbilicus. There are, how- 

 ever, still points in the generative economy of tbe monotremes which 

 remain to be determined by actual observation, viz. the manner and 

 •season of copulation, the period of gestation, the nature and succession 



