ZOOLOGICAL LITERATURE. 
If this be true, the larva of the trilobite ought to have quitted 
the ovum in the Nauplius form. 
The researches of Barrande have shown the existence of 
minute bodies which he and palaeontologists generally believe to 
have been the larva of the Trilobite. The one great law that is 
manifest as common to the Nauplius and the Zoea forms is, that 
progressive development commences at both extremities of the 
animal. The pleon and cephalon alone are present, with some 
of their appendages, previous to the appreciable presenee of the 
pereion, which is developed after the larva quits the ovum. W e 
find nothing in the development of tlie larva of the Trilobite 
that is incompatible with this idea. In the earliest stage the 
young trilobite consists of two nearly equal ( ivisions, tlie inci- 
pient features of the great cephalon and caudal shields. If (and 
we think it a not untenable hypothesis) these little bodies were 
supplied with three pairs of appendages and a central eye, all of 
which are merely deciduous organs, we should have an animal 
that would differ in nothing essentially from the Nauplius form 
of recent Crustacea. 
Independent of any interest that may attach itself to the 
arguments of Dr. Muller, some of which his opponents may not 
be inclined to accept, the memoir is one that every student in 
carcinology must study with interest, even though most of the 
faets have already been published in the author^s memoirs on 
the Prawns and other Crustacea. 
•The industrious Hr. G. O. Sars has published another memoir 
of his researches upon the Crustacea found in Norwegian fjords 
and lakes. (Beretning om en i Sommeren 1863 foretagen 
Zoologisk Reise i Christiania Stift ; 1864.) 
His present communication is the result of an excursion 
made in the neighbourhood or district of Christiania during the 
summer of 1863, in which he directed his attention first towards 
throwing as much light as possible upon the marine Crustacea, 
of the arctic type, which had been found in the great inland 
Scandinavian lakes. 
Although he visited many places, he sojourned longest in the 
vicinity of Lake Mjosen, since it seemed to give promise of a 
greater amount of information. From this lake he had pre- 
viously obtained a specimen of Mysis oculata of Fabricius, and 
by dredging in the deeper parts he hoped to get evidence of the 
other two marine forms, namely Gammarus loricatus and Idotea 
entomon, which has been taken in the lakes of Sweden, but not 
yet noticed by him. Lake Mjosen appears to be much deeper 
than he anticipated, being, at its greatest depth, nearly 2000 feet 
in the line of the channel. 
The bottom of the lake consisted of a dark-coloured mud, 
formed by the debris of decayed timber. In the line of the 
