I APPINITIES 31 
There are other points in which Balanoglossus specially resembles 
Amphioxus, such as the early development, the mode of formation 
of the body-cavities,, and the presence of numerous generative 
organs. 
All these, taken together, make it necessary to consider 
carefully the claims of Balanoglossus to relationship with the 
ancestors of Vertebrates in making any speculations on this 
interesting problem. 
However improbable it may appear at first sight, it is 
possible to hold the view that Balanoglossus is related at the 
same time to Vertebrates and to Starfishes and other Echino- 
derms. The similarity between a young Tornaria and a young 
Bipinnaria-larva of a Starfish is so great as to have misled even 
Johannes Miller. The more obvious resemblances are the almost 
identical course of the longitudinal ciliated band in the young 
stages, and the presence of a dorsal pore. The Echinoderm- 
larva is not, however, provided with eye-spots, nor has it the 
posterior, or transverse, ciliated band of Tornaria. 
Recent studies on the development of Echinoderms? have 
made it probable that the five body-cavities of Balanoglossus are 
represented in the larvae of those animals; and this materially 
strengthens the probability of the view that the respective adults 
are also allied® It may be added that the relationship which 
appears to be indicated is between Balanoglossus and the bilateral 
ancestors from which the radially-symmetrical Echinoderins are 
probably descended. 
In comparing the Enteropneusta with the Pterobranchia, the 
disproportionate size of the trunk of Balanoglossus may perhaps 
be explained by assuming that the region of the third body- 
cavities has been enlarged since Balanoglossus branched off from 
the ancestral stock* The approximation of the anus to the 
mouth in Pterobranchia is perhaps the result of their tubicolous 
habits.’ In the position of the central nervous system in the 
skin of the collar, Cephalodiscus appears to be more primitive 
1 See MacBride, Quart. J. Mier. Sci. xl. 1898, p. 589 ; xliii. 1900, p. 351. 
2 Bury, Quart. J. Micr. Sci. xxix. 1889, p. 409; xxxviii. 1896, p. 125 ; MacBride, 
tbid. xxxviii. p. 8395 ; Masterman, 7. R. Soc. Edinb. xl. Pt. ii. No. 19, 1902, p. 403. 
3 This view was definitely formulated by Metschnikoff in 1881 (Zool. Anz. iy. 
1881, pp. 139, 153). 
+ Cf. Morgan, J. Morphol. vy. 1891, p. 445; ix. 1894, pp. 64-66. 
> Cf. Lang, Jena. Zeitschr. xxv. 1891, p. 1. 
