s, and metamorphosis and
parthenogenesis, and perceive that they are but the terms of a single
series. By the acceleration in the development of a single set of organs
(the reproductive), no more wonderful than the acceleration and
retardation of the other systems of organs, so clearly pointed out in
the embryos of Platygaster and its allies, we see how parthenogenesis
under certain conditions may result. The barren Platygaster larva, the
fertile Cecidomyia larva, the fertile Aphis larva, the fertile
Chironomus pupa, the fertile hydroid polype, and the fertile adult queen
bee are simply animals in different degrees of organization, and with
reproductive systems differing not in quality, but in the greater or
less rapidity of their development as compared with the rest of the
body.

Another interesting point is, that while the larvae vary so remarkably in
form, the adult ichneumon flies are remarkably similar to one another.
Do the differences in their larval history seem to point back to certain
still more divergent ancestral forms?

These remarkable hyper-metamorphoses remind us of the metamorphosis of
the embryo of Echinoderms into the Pluteus-and Bipinnaria-forms of the
starfish, sea urchins and Holothurians;[24] of the Actinotrocha-form
larva of the Sipunculoid worms; of the Tornaria into Balanoglossus, the
worm; of the Cercaria-form larva of Distoma; of the Pilidium-form larva
of Nemertes; and the larval forms of the leeches;[25] as well as the
mite Pentastomum, and certain other aberrant mites, such as Myobia.

While Fritz Mueller and Dohrn have considered the insects as having
descended from the Crustacea (some primitive zoea-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 Myriopods) 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 po