INDUSTRIAL PROGRESS DURING THE YEAR 1875. cxcix 



their backs downward, rather than to those of Kowalevsky 

 and others, who trace the line through the Ascidians and the 

 lancelet. So far from being the representative of the orig- 

 inal vertebrates, the Amphioxus is regarded by Dr. Dohrn 

 as a degenerate descendant of the cyclostomous fishes, and 

 the so-called larvse of the Ascidians are the result of a still 

 longer-continued process of degradation. 



On account of these and other speculations, renewed at- 

 tention is being paid to a study of the embryology and 

 anatomy of Amphioxus, the lancelet. Mr. Balfour considers 

 that it is not necessary to conclude that Amphioxus itself 

 was the ancestor of the vertebrates, but merely that the ear- 

 liest stages of development of this supposed vertebrate an- 

 cestor were similar to those of Amphioxus. The egg of 

 Amphioxus differs from that of other vertebrate animals in 

 having less food-material or yolk, and Balfour thinks that 

 this accounts for the differences in the early stages of the 

 embryo. Still he thinks that all the modes of development 

 found in the higher vertebrates are to be looked upon as 

 modifications of that of Amphioxus. One common feature 

 which appears prominently in reviewing the embryology of 

 vertebrates as a whole is the derivation of the middle germ- 

 layer (mesoblast) from the third or inner layer (hypoblast), 

 though it should be stated that so high an authority as 

 Kolliker thinks that the middle layer is derived from the 

 outer one. Among the invertebrates, however, the middle 

 germ-layer is derived from the inner germ-layer. 



Professor Huxley publishes meanwhile a note upon the 

 " brain and skull " of Amphioxus. By reason of the sup- 

 posed absence of renal organs, and of any proper skull and 

 brain, Agassiz was led to separate the lancelet from all other 

 fishes ; and Haeckel, going farther, made a distinct division 

 of the Vertebrata (Acrania) for its reception; while Semper, 

 in a lately published paper, separates it entirely from the 

 vertebrates. Huxley now describes what he believes to be 

 the representative of the ducts of the Wolffian bodies, or 

 "primordial kidneys" of the higher vertebrates, in Amphi- 

 oxus, and he also endeavors to point out that, although Am* 

 phioxus has no completely differentiated brain or skull, 

 "yet it possesses very well-marked and relatively large di- 

 visions of the cerebro-spinal nervous axis and of the spinal 



