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Updated: May 29, 2025
Galton's biometrics and eugenics is a return to nature, a keen scrutiny of human beings, which is really an orderly fruition of that of the same author's "Art of Travel." Similarly, Mr. Weismann that he can plague his adversaries with the small but literal and concrete mice and hydroids and water fleas with which his theories began?
We will first compare the three Orders of Acalephs, Hydroids being the lowest, Discophorae; next, and the Ctenophorae highest. The fact that these animals have no popular names shows how little they are known.
Beside the Jelly-Fishes arising from Hydroids, there are many others resembling these in all the essential features of their structure, but differing in their mode of development; for, although more or less Polyp-like when first born from the egg, they never become attached, nor do they ever bud or divide, but reach their mature condition without any such striking metamorphoses as those that characterize the development of the Hydroid Acalephs.
The modern Coral animals are chiefly Polyps, but the prevailing Corals of the Silurian age were Acalephian Hydroids, animals which indeed resemble Polyps in certain external features, and have been mistaken for them, but which are nevertheless Acalephs by their internal structure; for, instead of having the vertical partitions dividing the body into chambers, so characteristic of the Polyps, they are divided by tubes corresponding to the radiating tubes of the Acalephs proper, these tubes being themselves divided at regular distances by horizontal floors, so that they never run uninterruptedly from top to bottom of the body.
This is one of the lower group of Radiates, known as Hydroids, and long believed to be Polyps, from their mode of living in communities and reproducing their kind by budding, after the fashion of Corals.
In the Hydroid-Medusae and Discophorae, instead of a simple digestive sac, as in the Hydroids, we have a cavity sending off tubes toward the periphery, which ramify more or less in their course.
I will begin with some account of the Hydroids, including the story of the alternate generations, by which they give birth to Medusae, while the Medusae, in their turn, reproduce the Hydroids, from which they spring. But first, a few words upon the growth of Radiates in general. There is no more interesting series of transformations than that of the development of Radiates.
This group of Hydroids retains the name of Coryne; and the Medusa born from it, Sarsia, has received, as I have said, the name of the distinguished investigator to whose labors we owe much of our present knowledge of these animals. Let us look now at another group of Hydroids, whose mode of development is equally curious and interesting.
From these ovaries a new brood of little embryos is shed in due time. There are other Hydroids giving rise to Medusae buds, from which, however, the Medusae do not separate to begin a new life, but wither on the Hydroid stock, after having come to maturity and dropped their eggs. Such is the Hydractinia polyclina.
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