52 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
It seems pretty certain tliat the radial symmetry of Echinoderms has 
been derived from bilateral symmetry, through the influence of a sedentary 
mode of life. The metamorphosis we now see is an expression of the 
course of phylogeny, subjected to exceedingly great distortion. The 
author inclines, therefore, to the view that the ancestral Echinoderm 
arose by the adaptive modification of a more primitive free-swimming 
form rather than the one that a larval form has been acquired for the 
purpose of distribution. 
Of the present groups of Echinoderms the earliest arising were the 
Synaptidae, then the ancestors of other Holothurians, later the ancestors 
of Grinoids, and latest the ancestors of Echinids, Ophiuroids, and 
Asteroids. The intermediate forms between each group probably 
persisted but a very short time, and the corresponding stages have, for 
the most part, been eliminated from the ontogeny. 
Most of the existing unstalked forms have been cenogenetically 
modified for a creeping life, the original excretory system assuming the 
locomotor in addition to the more early acquired sensory and respiratory 
functions. The early appearance of radial symmetry in the free swimming 
larva, shown by the radial outpushings of the hydrocoel wall at that 
stage of the ontogeny which is generally spoken of as the beginning of 
metamorphosis, may be regarded as precocious formation for the purpose 
of abbreviation of development. This last is carried to an extreme 
by the so-called viviparous Echinoderms. 
Development of Amphinra squamata.*— Mr. E. W. MacBride, who 
has already published a preliminary notice of the results of his investi- 
gations,! states that the following are the principal results to which he 
has been led. The primitive germinal cells are peritoneal, and from a 
portion of the rudiment which gives rise to them there is developed the 
ovoid gland, which is a solid organ. The axial and aboral sinuses are 
involutions of the coelom, and have no connection with the ampulla of 
the stone- canal or each other. The genital rachis is an outgrowth from 
the ovoid gland into the aboral sinus ; both kinds of cell, germinal 
and interstitial, which are found in the genital rachis, are formed in the 
ovoid gland. The germinal cells are formed from peritoneal cells 
directly, and there is no evidence of the transformation of the special 
cells of the ovoid gland into primitive germ-cells. 
From these observations it follows that Echinoderms agree with 
other Coelomata in the origin of their genital cells ; these have at first 
an unsymmetrical position in Echinoderms, and afterwards take on a 
radially symmetrical disposition in correspondence with the secondarily 
acquired radial form of the body ; this is in agreement with the classi- 
fications proposed by Prof. Jeffrey Bell | 8 in which the Echinoderma are 
divided into the two groups of Anactinogonidiata and Actinogonidiata. 
The origin of the genital cells adjacent to the stone-canal suggests a 
comparison of the origin of the same kind of cells near the nephridia of 
Annelids, though the author allows that the homology of the stone-canal 
with a nephridium has yet to be proved. 
With regard to the haemal system described by Prof. Ludwig, 
* Quart. Journ. Micr. Sci., xxxiv. (1892) pp. 129-53 (3 pis.), 
t See this Journal, 1892, p. 621. I Op. cit., 1891, p. 662. 
