256 MR GOODSIR ON THE ANATOMY OF AMPHIOXUS LANCEOLATUS. 



At the extremities of each pair of bifurcated ribs the abdominal vessel just de- 

 scribed gives off a primary branch, which passes along the edge of the rib, sending 

 secondary branches at regular intervals and at right angles to the other primary 

 branches on each side. Along the opposite sides of all the ribs another set of ves- 

 sels may be seen, passing on to the chorda dorsalis, enlarging as they advance, 

 and sending off secondary branches at right angles. When near the heads of 

 the ribs, these vessels anastomose in semicircular loops, the canals of which are of 

 large calibre, and the walls provided with distinct circular fibres. From the 

 angles between each of these loops, and continuous, therefore, with the primary 

 branches, smaller trunks pass on to the median line, and enter, opposite to their 

 fellow at the other side, into a small longitudinal vessel which runs along the 

 whole length of the chorda dorsalis, between the heads of the ribs, and on the 

 inferior surface of the inferior longitudinal ligament. This vessel is the Aorta, 

 and distributes arterial branches to the various parts of the body. 



Generative System. 



This system consists of a series of somewhat irregular, bean-shaped, granular 

 bodies, situated each on the inside of the inferior extremity of the ventral portions 

 of twenty or thirty of the muscular bundles of the middle third of the animal. 

 These masses are attached to the internal surface of the aponeurotic lining of the 

 abdomen, on the outside of the branchial chamber. No duct or outlet could be 

 detected. Each mass, under the microscope, displayed a congeries of cells of 

 various sizes, evidently incipient ova or sperm cells. The individual did not ap- 

 pear to be in season. 



Tegumentary System. 



The skin is remarkably thin, but tough ; and exhibits neither scales, pigment, 

 nor metallic lustre, except at the base of the dorsal fin, along which, or the upper 

 edge of the interspinous bones, a silvery band of considerable strength passes. 

 The skin, under the microscope, displays minute parallel striee, which occasionally 

 cross one another. The beautiful iridescent tints which it exhibits, both before 

 and after detachment, appear to be caused by these stria; ; and the same structure 

 probably produces similar phenomena in the aponeurosis which lines the cavity 

 of the abdomen. 



CONCLUDING REMARKS. 



At a very early period in the development of every vertebrated animal, the 

 cerebro-spinal axis presents the appearance of a white elongated streak. At the 

 same period, and in accordance with this simple condition of the nervous central 

 organ, the skeleton consists of a chorda dorsalis, and, very soon afterwards, of 

 some of the peripheral elements of the spinal column. A central organ of circu- 



