4.52 Retrospective Criticism. 
I think it demonstrable that the pearl is not the product of disease; an 
animal excretion, but moulded from the pearly matter of the shell; the cavities 
in the interior of the shell, and where the pearls are found to lodge, seem 
to go far to prove this. The vast size and great variety of form and colour 
occasionally presented concur in the conjectural probability. They are 
formed by the animal as plugs to stop up the enemies’ mine, — the circular, 
&c., perforations of the Venus lithéphagus, J/ytilus lithéphagus, Pholas dac- 
tylus, and Murex Brandaris, &c.— J. Murray. Carmarthen, April 2. 1830. 
Leather Coat Jack (Vol. IIL. p.80).— Sir, The following extract from 
Kirby and Spence’s Entomology, vol. iv. p. 189., will throw some light upon 
the history of this wonder-working individual, who appears to have been, 
by a feat almost as extraordinary, transformed by Mr, Rhind into an insect. 
“ But the grub of Eldphilus tenax (a drone-looking fly) affords a more sur 
prising instance of this power of counteraction : — an inhabitant of muddy 
pools, it has occasionally been taken up with the water used in paper- 
making, and, strange to say, according to Linné, has resisted without injury 
the immense pressure given to the surrounding pulp (4'n. Suec. 1799) ; like 
Leather Coat Jack, mentioned by Mr. Bell (Anatomy of Expression in 
Painting, 170.), who, from a similar force of muscle, could suffer carriages 
to drive over him without receiving any injury.” The circumstance men- 
tioned by Linnzeus is however more wonderful than the exploits of the above 
individual ; and the authority of the learned Swede is of so high a nature, 
that but little doubt can arise upon the narrative. —J. O. Westwood. 
Feb.'7, 1830. 
Ichneumonide. — Sir, It is a constant source of regret to the real lover 
of nature, that the more minute objects of the creation are generally looked 
upon by the professed general naturalist with apathy, even if they are not 
entirely disregarded, as though they were unworthy of attention and in- 
vestigation. Forgetful that the lowest insect or polype, even the meanest 
atom that lives, the Monas itself, derives importance from occupying a 
link in the great and complicated chain of the creation, such persons are 
contented to observe and study objects only which attract their attention 
by their splendour or size, or by the benefits or injuries which they discover 
them to be capable of bestowing or inflicting. It is not however to be 
denied that many, nay, the majority, of the more minute creatures exhibit 
“ the work of an almighty hand” in a far more wonderful and interesting 
manner than their larger brethren, whether we regard the brilliancy of their 
colouring, the peculiarity of their characters, or the exceeding singularity 
of their economy. Hence, from such inattention must obviously arise great 
confusion in the nomenclature of the objects ; and it has hence repeatedly 
occurred, that the most interesting observations have become lost to the 
student, from the circumstance of the object being either unnamed or mis- 
named. Of this confusion existing in the greatest degree, the minute 
families of hymenopterous insects have perhaps afforded the most preva- 
lent examples. And I cannot but regret that the communication of your 
correspondent T. H. (p.51.) has exhibited an additional proof of this 
confusion in his nomenclature of the object of his paper, namely, a very 
small species of ichneumon fly (Zchnetimon ovulorumof Linnzeus, Platygaster 
ovulorum of the fam. Proctotrtipide of Latreille. In the first place, it is 
to be observed, that the xame of the insect adopted by your correspondent, 
T. ovulorum, is sufficient of itself, from its reference to the economy of 
the species, to prove that it could not be applicable to the insect in ques- 
tion; the true Z. ovuldrum of Linnzus inhabiting, as the name implies, 
the eggs of lepidopterous insects. Your correspondent’s insect is in fact 
the /chnetimon glomeratus of Linneus, and its history has been investi- 
gated by Reaumur, De Geer, Résel, &c. &c. In the second place, supposing 
that your correspondent’s insect were the true Zchneumon ovulorum, or 
that he were correct in referring the egg-feeding ichneumon to the genus 
