626 DE. 11. CHARLTON BASTIAN ON THE ANATOMY AND PH TSIOLOGT 



the adult Echinoderm is produced from and out of this ciliated larva, affords a process 

 of development certainly varying as much as possible from the simple and direct evolu- 

 tion of the young animal from the yelk-mass, such as obtains amongst the Nematoids 

 both free and parasitic ; but such diflfierences in tlie method of development of apparently 

 nearly allied animals may be paralleled by the discrepancies in this respect existing 

 between the simple Ilydroe and the various families of the Compound Hydroida, and also 

 between the different families of Annelida. Concerning these latter Dr. Carpkxtkr 

 remarks *, " In the history of the development of the several orders of the Annelida 

 there exists a very marked diversity ; for whilst the young of the Terricolce and Suctoria 

 do not usually issue from the egg until they have acquired the characteristic forms of 

 the parent (although the number of segments may be subsequently augmented), the 

 embryos of the Dorsibrancliiata and Tuhicolce come forth in a state of far less advance- 

 ment, and only acquire their perfect form by such a series of changes as deserves the 

 designation of a metamorphosis." 



It remains to be pointed out, as before alluded to, that although the quinary airange- 

 ment of organs and parts is so prevalent amongst the Echinoderms, it is far from being 

 invariable; for, as remarked by Professor Foebes, "monstrous starfishes and urchins 

 often appear quadrate and have their parts fourfold, assuming the reigning number of 

 the Actinodermata," or Polypes. In the Nematoids, too, we meet with a quadrate mixed 

 with a ternate type of formation. The lateral and median lines radiate crucially from 

 the mouth and extend along the body, alternating with four great longitudinal muscles ; 

 but whilst we have here a radiate an-angement, which may also be considered bilateral, 

 this approach to a bilateral symmetry is disturbed by the fact that the oesophageal canal 

 in the Nematoids is almost invariably triquetrous, that the number of teeth in the pha- 

 ryngeal cavity of the free Nematoids, when such exist, is generally three, and that the 

 same number applies to the cephalic lobes of the Ascarides, and a multiple of it to those 

 of the Spiropterce. As another notable instance of deviation from a bilateral symmetry, 

 may be cited the remarkably unsymmetrical distribution of the peculiar transverse pairs 

 of vessels existing in some members of the genus Ascaris-^. 



By reason of these various resemblances, though more especially on account of the 

 remarkable identity in the structure and arrangement of their nervous systems, I think 

 it most in accordance with the nature of ascertained facts to look upon the Nematoids 

 as close allies of the Echinodermata — more closely allied to them, in fact, than to the 

 Scolecida. Whilst, however, it would be difficult to assign to the order Nematoidea a 

 zoological position in either of these classes, there can be little doubt that their organi- 

 zation — uniting as it does, in a remarkable manner, some of the chief characteristics of 



* Princip. of Comp. Phpiol. 1854, p. 593. 



t Miller's Archiv. According to the descriptions given by Meissneh, the departure from the bilateral and 

 prevalence of a ternary arrangement must be stiU more striking amongst the Gordiace<t, since he describes in 

 these animals throe great longitudinal muscles instead of four, alternating with three cellular bands apparently 

 homologous with the lateral bands of the Nematoids. 



