REPORT ON CEPHALODISCUS DODECALOPHUS. 37 



parallel in the life-history of Cephalodiscus, not even an embryonic approach occurring 

 in either form. The anus in Balanoglossus is posterior and terminal at all stages. The 

 relations of the dorsal and ventral surfaces in the two forms are also at variance. Buds 

 again, are unknown in either Phoronis or Balanoglossus, and in both the eggs are very 

 numerous and small, whereas in Cephalodiscus they are few and very large. 



The main resemblances between Cephalodiscus and Bcdanoglossus lie in the structure 

 of the skin, the presence of three body-cavities (disk, collar, and body proper), the 

 proboscis or disk-pores, collar-pores, gill-slits, and rudimentary notochordal structure, 

 and they are of a most interesting and suggestive character ; and as ]\Ir. Harmer, whose 

 valuable researches on the Entoproctous Polyzoa are well known, has most ably studied 

 these features and formed independent conclusions, I have thought it best to give his 

 views in his own words as an Appendix. These will show how difficult it is in some 

 cases to draw clear lines of distinction — so intimately are the several characters, in 

 apparently diverse groups, blended. In a former paper ^ I had observed with regard to 

 Phoronis and Balanoglossus — " If indeed the branchial skeleton supporting the vessels 

 (of Phoronis) were thrown in, and arranged at the sides of the anterior region of the 

 body, so that the water would enter by lateral slits to aerate the circulating fluid, and 

 the digestive canal enlarged and attached as a single tube to the body-wall, a form 

 resembling Balanoglossus would be indicated." It has to be borne in mind also that 

 Alexander Agassiz thought that the latter resembled the Tunicates from the nature of 

 the gills and their mode of formation, in opposition to the views of Kowalevsky and others, 

 who placed its affinities with the Annelids proper. 



Perhaps Balanoglossus may at present be ranged near the Aspidophorous group of 

 the Polyzoa, for though Metschnikoff's view that it approaches the Echinoderms rests on 

 the remarkable fact that in Tornaria the original evagination from the gut is on the left 

 side, just as in Asteroid larvae the water-vessel is developed from the left primitive 

 diverticulum (Bateson), yet there are stronger reasons for associating it with other groups 

 as above mentioned. 



1 Proc. Boy. Soc. Edin., Session 1880-81, vol. xi. p. 217. 



