SCIENTIFIC SUMMARY. 
137 
form, however, and the hairs which cover it giving it the characters of a 
dipterous larva. After a while it becomes quiescent, and a second larva 
is developed within it, which in its turn becomes converted into a nymph. 
Hence the author concluded that this was an instance of development 
through the medium of nurses , as Steenstrup termed them. He now 
corrects the error into which he had thus fallen, and instead of regarding 
it as an instance of metagenesis, he considers that the first larva passes 
into the second stage by a change of skin, and he therefore looks on the 
process as a case of hypermetamorphosis. 
The Embryology of Echinoderms. — A valuable compilation with this 
title has been made by Professor Wyville Thomson. It includes the 
researches of Sars, 0. F. and J. Muller, Koren, Danielssen, &c., together 
with the compiler’s own investigations into the development of Comatula, 
Synapta and Asteracanthion. The end in view appears to be the 
endeavour to trace some common principle correlating the various modi- 
fications which are presented in the course of the developmental processes 
by the several members of the group. The writer regards the Echinoder- 
mata as constituting a group which is as much entitled to the designation 
of sub-kingdom as Coelenterata or Annulosa ; for although they exhibit 
a decided relationship to the latter, yet “ they have maintained through 
the whole series of geological periods a high degree of importance, and at 
the same time a singular compactness as a natural group. 5 ’ This group 
presents some very remarkable points in the history of development. 
From a single egg two distinct organisms are produced which, apparently, 
have all the important characters of a true animal. These two beings are 
entirely different , one appearing to be related to the Annulosa, whilst the 
other, which is subsequently formed within the first, becomes the perfect 
Echinoderm. In Bipinnaria we have an instance of an organism developed 
from the germ-mass, and carrying on an independent life before the 
appearance of the genuine Echinoderm. To a production of this kind 
Professor Thomson applies the expression Pseudembryo ; and all the 
appendages which relate to it, even though they possess none of the 
characters of a perfect animal, he styles pseudembryonic appendages . In 
all Asterid germs there is a fusion of the whole or a part of the germ-mass 
into a layer of the peculiar structureless histological element — sarcode — 
which possesses, as it were, an individuality of its own quite apart from the 
true embryo. The writer lays especial stress upon this conclusion ; he 
is not content with the supposition that this layer is merely an equivalent 
of protoplasm ; for him, it possesses a peculiar vital activity , which has not 
been fairly recognised. W e cannot see why it is necessary to suppose that it 
is more endowed with special powers than the periplast, which in one case 
can become a bone, and in another a sinew. — Vide “ Nat. Hist. Rev.’ 5 
A New Species of Coccus. — M. Le Mulier has addressed a note to the 
French Academy, announcing the discovery of a Coccus indigenous to 
Algeria, whose colour when bruised is like that of the insect which is 
familiarly known as cochineal (C. Opuntise), and which he thinks might 
with advantage be employed as a colour. It is found chiefly on umbelli- 
ferous plants, and is easily recognized on account of the beautifully white 
cottony down with which its body is clothed. If it were thought desirable 
