94 Miscellaneous. 



On the Relationship of the Vertehrata and Annelida. 

 By C. Semper. 



It is well known that the Ascidia are rejjarded with Kupfer and 

 Kowalevsky as the nearest relatives of the Vertehrata ; and this 

 opinion is supported hy the analoj^ous mode of ])rodiiction of tho 

 nerve-cord and the presence of a chorda between it and the intes- 

 tine in both jrroups of animals. But it is forgotten that the Verte- 

 hrata are sejrmented animals, while the Ascidia arc not so : the sole 

 indication of a sepjmentation in the latter appears to He in the oc- 

 currence of spinal nerves in the tail and hinder jiart of the body of 

 the larva of Ascidia mentula, as affirmed by Kupfer. 



This gap is now filled in a most unexpected manner by the dis- 

 covery of segmental organs in Selachian embryos. In Acanthias, 

 Centrina, and Sct/UiKm I have found funnel-shaped openings leading 

 into ciliated ducts in connexion with the primitive kidneys ; they 

 are placed, one pair in each segment (metamere), right and left of 

 the mesentery, along the whole of the body-cavity. They are pro- 

 duced by depression of the peritoneal epithelium, and are only 

 secondarily connected with the lateral canals of the primitive renal 

 duct, which also issue segmentally. The funnels in Acantliias are 

 very large ; and their cilia vibrate strongly. In Centrina and Acaji- 

 thias they may be detected by the lens even in nearly mature em- 

 bryos ; in Soflliiim, on the contrary, they disappear very early. 

 In Acantliias the ovary is developed without any participation of 

 the segmental organs ; but in the male the seminal duct seems to 

 become developed ])y a peculiar process of budding and amalga- 

 mation of the segmental funnels. 



Except in a single point, the comparison to the segmental 

 organ of an annelide may be completely carried out. In the one, as 

 in the other, they are repeated in pairs in the segments of the body : 

 they have a ciliated funnel opening freely into the cavity of the 

 body ; the ciliated duct springing from this leads into a glandular 

 segment (in the Vertebrates to the Malpighian body or primitive 

 kidney) ; they are in intimate relation with the genital organs; and, 

 lastly, they are produced in their glandular and infundibular portion 

 from the mesoderm. The sole distinction consists in the mode of 

 opening of these excretory organs : in the Annelida each seg- 

 mental organ opens separately in the corresponding segment of the 

 body ; in the Vertehrata they unite with the primitive i-enal duct, 

 which in the Selachia, as in the Teleostea, is a product of the peri- 

 toneal epithelium. This contradiction cannot, however, be used as 

 an argument against the comparison of the two sets of organs, as 

 the union of the glandular part with the efferent ducts is in both 

 cases produced secondarily by the coalescence of the original separate 

 rudiments ; moreover the so-called aquiferous vessels of the Rota- 

 toria are universally compared to the segmental organs of tho 

 Vermes, although in the former, just as in the Vertehrata, two effer- 

 ent ducts opening into the cloaca take up the secretion of the glands, 

 which open by several funnels into the body-cavity. 



It might appear that a statement of Gegenbaur's is to be referred 



