I02 



NATURE 



[Dec. lo, 1874 



Amphioxus, which so closely resembles an Ascidian in 

 its development, has a perivisceral cavity which essentially 

 corresponds with the atrium of the Ascidian, though it is 

 formed in a somewhat different manner. One of the 

 most striking peculiarities in the structure of Amphioxus 

 is the fact that the body wall (which obviously answers to 

 the somatopleure of one of the higher Vertebrata, and 

 incloses a " pleuro-peritoneal " cavity, in the walls of 

 which the generative organs are developed) covers the 

 branchial apertures, so that the latter open into the 

 "pleuro-peritoneal" cavity. This occurs in no other 

 vertebrated animal. Kowalewsky has proved that this 

 very exceptional structure results from the development 

 of the somatopleure as a lamina which grows out from 

 the sides of the body and eventually becomes united with 

 its fellow in the middle ventral hne, leaving only the so- 

 called " respiratory pore " open. Stieda has mentioned the 

 existence of the raph^ in the position of the line of union 

 in the adult animal. Rathke described two " abdominal 

 canals" in Amphioxus j and Johannes Miiller, and more 

 recently Stieda, have described and figured these canals. 

 However, Rathke's canals have no existence,and what have 

 been taken for them are simply passages or semi-canals 

 between the proper ventral wall of the abdomen and the in- 

 curved edges of two ridges developed at the junction of the 

 ventral with the lateral faces of the body, which extend 

 from behind the abdominal pore where they nearly meet, 

 to the sides of the mouth. Doubtless, the ova which 

 Kowalewsky saw pass out of the mouth, had entered into 

 these semi-canals when they left the body by the abdomi- 

 nal pore, and were conveyed by them to the oral region. 

 The ventral integument, between the ventrolateral laminse, 

 is folded, as Stieda has indicated, into numerous close-set, 

 longitudinal plaits which have been mistaken for muscular 

 fibres, and the grooves between these plaits are occupied 

 by epidermic cells, so that, in transverse section, the in- 

 terspaces between the plaits have the appearance of 

 glandular coeca. This plaited organ appears to repre- 

 sent the Wolffian duct of the higher I'crtcbrata, which, 

 in accordance with the generally embryonic character of 

 Ampliioxus, retains its primitive form of an open groove. 

 The somatopleure cti Amphioxus therefore resembles that 

 of ordinary Vertebrata in giving rise to a Wolffian duct 

 by invagination of its inner surface. But the Wolffian 

 duct does not become converted |into a tube, and its 

 dorsal or axial wall unites with its fellow in the raphd of 

 the ventral boundary of the perivisceral cavity. 



In all the higher Vertebrata of which the development 

 has yet been traced, the " pleuro-peritoneal " or perivisceral 

 cavity arises by an apparent splitting of the mesoblast, 

 which splitting, ho\vever,does not extend beyond the hinder 

 portion of the branchial region. But, in many I'ertcbrata, 

 (e.g., HoIocepJiali, Ganoidci, Teleostei, Amphibia) a pro- 

 cess of the integument grows out from the region of the 

 hyoidean arch, and forms an operculum covering the 

 gill-cleft. In the frog, as is well known, this opercular 

 membrane is very large, and unites with the body wall 

 posteriorly, leaving only a " respiratory pore " on the left 

 side, during the later periods of the tadpole's life. Here 

 is a structure homologous with the splanchnopleure of 

 Amphioxus ; while, in the thoraco-abdominal region, the 

 splanchnopleure appears to arise by splitting of the meso- 

 blast. Considering what takes place in Amphioxus, the 



question arises whether the " splitting " of the mesoblast in 



the Vertebrata may not have a different meaning from the 

 apparently similar process in the Artliropoda, Aniielieia, 

 and Mollusca ; and whether the pericardium, pleura, and 

 peritoneum are not parts of the epiblast, as the atrial tunic 

 is of the epiblast of the ascidians. Further investigation 

 must determine this point. In the meanwhile, on the 

 assumption that the " pleuro-peritoneal " cavity of the 

 Vertebrata is a \'irtual involution of the epiblast, the 

 peritoneal aperture of fishes becomes truly homologous 

 with the "respiratory pore" of Ampliioxus : and the 

 Wolffian ducts and their prolongations, with the Miillerian- 

 ducts, are, as Gegenbaur has already suggested, of the 

 same nature as the segmental organs of worms. 



The division of Metazoa without an ahmentary cavity 

 is established provisionally, for the Cestoicica and Acan- 

 Ihoeephala, in which no trace of a digestive cavity has 

 ever been detected. It is quite possible that the ordinary 

 view that these are Gastrere modified by parasitism is 

 correct. On the other hand, the cases of the Nematoid 

 worms and of the Trematoda show that the most com- 

 plete parasitism does not necessarily involve the abortion 

 of the alimentary cavity, and it must be admitted to be 

 possible that a primitive Gregariniform parasite might 

 become multicellular and might develop reproductive 

 and other organs, without finding any advantage in an 

 alimentary canal. A purely objective classification will 

 recognise both these possibilities and leave the question 

 open. 



THE "TIMES" ON THE IMPORTANCE OF 

 SCIENTIFIC RESEARCH 



[In an article which appeared in yesterday's Times, 

 occasion is taken of the occurrence of the Transit of 

 Venus to point out the great activity now being displayed 

 by foreign nations in the prosecution of abstract scientific 

 inquiries, and the necessity of retaining England's old 

 pre-eminence in this respect. The article is so important 

 as indicating the growing importance which is being 

 attached to research, that we reproduce a great part 

 of it in our own columns, because the considerations 

 urged by the Times lead to a conclusion of no uncertain 

 sound. As England has nobly in the past, when she 

 was almost alone, led in the search after abstract scien- 

 tific truths, it behoves her now that she is by no means 

 alone and has to compete with rivals who have shown by 

 their Transit expeditions and by many other signs what 

 their opinion is on this matter, to more than redouble 

 her old efforts, if she wishes to retain the position she 

 has won by the accumulated work of centuries. — Ed. 

 Nature.] 



THE astronomer's point of view is by no means 

 the only one of general interest connected with 

 the recent Transit. We have, first of all, the re- 

 markable spectacle of trained observers of almost all 

 nationalities — observers sent out by England, the United 

 States, France, Germany, Italy, and Holland — dis- 

 tributed among some seventy stations, some of them 

 the most inhospitable islands of the Southern seas, en- 

 gaged upon one of the most abstract inquiries which can 

 be imagined. The anxiety of the various European and 

 the American Governments to contribute towards the 

 solution of the problem can perhaps best be shown by 

 indicating the stations occupied this morning by the 



