ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 417 



Tliis first appears as a small elevation just behind and to the 

 left of the end of the endostyle ; it soon consists of two cell-tubes, 

 one within the other, and having the intermediate space filled by a 

 cell-mass. The outer layer of the stolon is clearly an evagination of 

 the ectodermal tegumentary epithelium of the embryo ; the space is 

 a continuation of the primary coelom, and the cells that fill it are 

 mesodermal in origin. Huxley's account of the endoderm of the 

 stolon as arising from the pericardium of the embryo is explained by 

 the observation that the endodermal evagination extends to and fuses 

 with the pericardium ; the characters of the mesoderm are described 

 in detail, and the author then passes to an account of the growth 

 and torsion of the stolon ; as it grows it surrounds the hind-body, and 

 as it twists its distal end comes to lie ventrally to the nucleus. As 

 the stolon and its buds grow, the solitary animal also increases con- 

 siderably in size. The buds are not formed by special outgrowths of 

 the stolon, but by metamorphoses of the whole of it ; the ectodermal 

 tube of every young bud contains six separate structures ; neurally is 

 the ganglion, two endodermal sacs, two mesodermal bands, and 

 hfemally the ovary and rudimentary oviduct ; along the whole 

 length of the germ-stock there extends two blood-passages common to 

 all the buds, and these, enclosed by a flattened epithelium and a 

 layer of cellulose, lead directly into the lacunar system of the embryo ; 

 they are separated by two horizontal layers of cells which are derived 

 from the endodermal tube of the stolon. Owing to the presence of 

 the endothelial wall the blood cannot pass directly into the young 

 buds. 



In the last period of development the primitive connection between 

 the separate individuals is lost, and they are only connected by a 

 fresh set of attaching processes. This separation becomes so com- 

 plete that there is no structure which is common to all or even to 

 several chain-salpae ; the young animals cut themselves off from the 

 region of the two blood-passages, so that these come to lie quite out- 

 side the body of the Salpee. The tube in which they are enclosed 

 may be regarded as the remains of the stolon, and it gradually 

 decreases in size. By the outgrowth of the attaching processes the 

 chain-stage becomes possible, and the single structure becomes con- 

 verted into a number of parts. The histological and structural 

 changes which take place during this stage of development are fully 

 described, and the whole may be thus summed up : — 



The ectoblast of the embryo forms the ectodermal cell-tube of the 

 stolon, the tegumentary epithelium, and the outer cellulose mantle of 

 the chain-salpa; the mesenchym of the nucleus, which is perhaps 

 partly derived from embryonic mesoblast, gives rise to the two paired 

 lateral cords (which divide into the lateral end which belongs to that 

 side of the stolon on which the chain-individuals will lie later, and 

 the haemal part of the opposite cord), the cord of the ovary, and the 

 nerve-tube of the stolon ; the lateral cord forms the inner cellulose 

 mantle, the connective-tissue cells, the muscular bands and fibre-cells, 

 the blood-cells, the dorsal wall of the gill-band, and the wall of the 

 cloaca in the chain-salpa ; the htemal part forms the pericardium, heart, 



