THE WORMS THE ANCESTOUS OF INSECTS. 169 



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

 form larva of Distoraa; of the Pilidium-form larva of Nemertes; 

 and the lurval forms of the leeches ;* as well as the mite Peutas- 

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



While Fi'itz Miiller and Dohrn have considered the insects as 

 having descended from the Crustacea (some primitive zoea- 

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

 these egg-parasites as a proof, we cfiuuot but think, in a subject 

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

 brought out by Gauin 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 Ci'ustacea, 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 



Foundings of tliese animals in the free swimming condition. Merely to point out 

 the diflerences in tlie mode of development of animals is an interestiug matter, 

 and one could do worse things, but the philosophical naturalist camiot rest here. 

 He must seek.how these differences were brought about. 



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

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

 to consider tlie tirst indications of tlie 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 Ecliinoderms is the same iu 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 tlie 

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

 sine) aud certain bristle-bearing worms (Sa'uuris, I^umbriculus and Uaxes), aud 

 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 foruiation of the primitive band in the leeches and 

 earth worms being mucli like that of insects. This confirms the view of Leuckuit 

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

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

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

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

 allow. The singular EchiuoUeres has some remarkable Arthropod characters. 

 15 



