THE WORMS THUS ANCESTORS OP INSECTS. 169 



of the Tornaria into Balanoglossus, the worm ; of the Cercaria- 

 form larva of Distoma; of the Pilidium-form larva of Neraertes; 

 and the larval forms of the leeches ;* as well as the mite Pentas- 

 tomum, and certain other aberrant mites, such as Myobia. 



While Fritz Miiller and Dohrn have considered the insects as 

 having descended from the Crustacea (some primitive zoe'a- 

 form), and Dohrn has adduced the supposed zoea-form larva of 

 these egg-parasites as a proof, we cannot but think, in a subject 

 so purely speculative as the ancestry of animals, that the facts 

 brought out by Ganin tend to confirm our theory, that the 

 ancestry of all -the insects (including the Arachnids and Myrio- 

 pods) should be traced directly to the worms. The development 

 of the degraded, aberrant Arachnidan Pentastomum accords, in 

 some important respects, with that of the intestinal worms. 

 The Leptus-form larva of Julus, with its strange embryological 

 development, in some respects so like that of some worms, 

 points in that direction, as certainly as does the embryological 

 development of the egg-parasite Ophioneurus. The Nauplius 

 form of the embryo or larva of nearly all Crustacea, also points 

 back to the worms as their ancestors, the divergence having 

 perhaps originated, as we have suggested, in the Rotatoria. 



While the Crustacea may have resulted from a series of 

 prototypes leading up from the Rotifers (Fig. 198), it is barely 



roundings of these animals in the free swimming condition. Merely to point out 

 the differences in the mode of development of animals is an interesting mutter, 

 and one could do worse things, but the philosophical naturalist cannot rest here. 

 He must seek how these differences were brought about. 



* Leuckart, in his great work, "Die Menschlichen Parasiten," p. 700, after the 

 analogy of Hirudo, which develops a primitive streak late in larval life, ventures 

 to consider the first indications of the germ of Nemertes in its larval, Pilidium 

 form as a primitive streak. He also suggests that the development of the later 

 larval forms of the Echinoderms is the same in kind. 



Moreover, nearly twenty years ago (1854) Zaddach, a German naturalist, con- 

 tended that the worms are closely allied in their mode of development to the 

 insects and crustaceans. He compares the mode of development of a leech (Clep- 

 sine) and certain bristle-bearing worms (Sa^nuris, Lurnbriculus and Uaxes), and 

 we may now from Kowaleusky's researches (1871) add the common earth worm 

 (Lumbricus), in which there is no such metamorphosis as in the sea Nereids^to 

 that of insects; the mode of formation of the primitive band in the leeches and 

 eartli worms being much like that of insects. This confirms the view of Leuckart 

 and Ganin, who both seem to have overlooked Zaddach's remarks. Moreover, the 

 rings of the harder bodied worms, as Zaddach says, contain chitlne, as in the in- 

 sects. Zaddach also enters into farther details, which in his opinion ally the 

 worms nearer to the insects than many naturalists at his time were disposed to 

 allow. The singular Echiuoderes has some remarkable Arthropod characters. 

 15 



