OF THE HYDROMEDUS^E. 385 



and the origin of the endoderm. Haeckel and Fritz Muller say that the central capsule 

 becomes the sub-umbrella, from the walls of which the digestive tract is subsequently 

 formed ; Fol and Metschnikoff hold that the central capsule is the digestive cavity, and that 

 the sub-umbrella is an ectodermal structure of later origin; while Kowalevsky claims that 

 the central capsule is neither endoderm nor sub-umbrella, but that it breaks down and 

 becomes the gelatinous substance of the bell. 



In the summer of iSSii I studied the embryology of Liriope scutigera in order to decide 

 between these conflicting views, and quickly satisfied myself of the correctness of the 

 accounts of Fol and Metschnikoff. 



While I was engaged in this work I received Metschnikoff's last paper (52) dated 

 Dec. 30, 1881, giving an account of his renewed study at Naples of the embryology 

 of Liriope euryhea, Haeckel, and Carmarina fungiformis, Haeckel, resulting in the com- 

 plete verification of the account which he published in 1874. 



The next paper in historical order, "On Young Stages of Limnocodium and Geryo- 

 nia," by Ray Lankester (45), is a very noteworthy example of "deductive biology;" for 

 while the title would lead us to expect new observations on the young stages of the 

 G-eryonidse, the paper contains nothing to show that the author has ever seen a Gery- 

 onid, either young or adult, and his statement (44) that the tentacles of the Trachomc- 

 dusse are solid would hardly be made by any one who had examined an adult Geryonid; 

 nor for that matter would anyone who is familial- with Eucope venture the statement 

 that the Leptomedusae all have hollow tentacles. In this connection see Ilamann (32) 

 and the Hertwigs (69, p. 72). 



It is true that the paper does contain diagrammatic figures, page 200, to illustrate the 

 development of the Trachomedusa\ but they are purely imaginary and unlike anything 

 which has ever been observed, for the author has undertaken the very dangerous task 

 of constructing embryology upon general ground rather than from observation. 



As his theoretical views bring him into conflict with the careful observations of Fol 

 and Metschnikoff, he attempts to show that there is a "substantial disagreement" between 

 their accounts, and he does not hesitate to assert that "Fol has completely failed to give 

 even an approximately correct account of the matter," while Metschnikoff's account is 

 "erroneous." 



The same author had published, a few months before, an account of an interesting me- 

 dusa which was found in very great numbers, at various stages of growth, in a tank in which 

 tropical water plants were cultivated in England. The medusa, Limnocodium, is remarka- 

 ble in many respects, as it is very different from all the known species, and has, so far as we 

 know, no close allies. Kay Lankester regards it as a Trachomedusa, although Allman, 

 •who described it on the same day in another place (70), considers it a Leptomedusa. 



In his second paper (45) Ray Lankester gives figures of young medusae which ^vw 

 found in the water with the adults, all of which were males, and although the young are 

 similar in all respects to the medusa-buds of hydroids, and quite unlike any medusa- 

 embryo which has ever been reared from the eggj he regards them as egg-embryos, and 

 constructs upon them a new view of the embryology of the Trachomedusse, although be 

 did not rear them from the egg, and gives no reason for believing that they are egg-em- 



