The BOOK 
- fame thing happens about the mufcles of the 
branchiez, Tab. XIV. fig. 1. ¢c,and rowing fins. 
From each little knot, Tab. XIV, fig. 1. ee, 
of the fpinal marrow, there conftantly iffue 
two flronger nerves, which unite and become 
more fwollen when they approach the fubfe- 
quent nerve ; for which reafon the {pinal mar- 
row appears every where divided and open. 
But while it is in its ftate of nature contained 
within the body, that gaping does notappear; be- 
caufe thenervesare there only fimply contiguous 
to each other, and do not therefore appear to be 
far diftant from each other; as I have fhewn 
in the fixth figure, Tab. XV. in which the 
fpinal marrow, as it is naturally contained in 
the body, and the fourteen annular incifions 
of the creature wherein the marrow lies are 
delineated. 
If any one has a mind to view the {pinal 
marrow, without hurting or injuring the crea- 
ture, let him fill the body with air blown in 
through the hinder part: for thus the marrow 
will be by the force of the {wollen inteftines 
fo ftrongly prefled againft the tran{parent skin, 
that one may conveniently view its natural 
fituation and form, even with the naked eye, 
as well as with a microfcope. But this con- 
trivance can be ufed in the males only. 
The {pinal marrow, as well as the other 
parts of the creature, has its air-pipes, and in- 
deed a great number of them; fo that the 
brain and nerves are contiaually as it were ven- 
tilated with injected air. Ido not doubt but 
the marrow has veins and arteries, though I 
never faw them; for in Silk-worms I have 
clearly feen various {mall veffels fpring from, 
and approaching to the heart, which I have 
even filled with a coloured liquid. But whe- 
ther they were veins or arteries, I cannot yet 
affirm. 
The f{permatic veflels, Tab. XIV. fig. 1. 
or genital organs, are as confpicuous in the male 
of thefe Worms, the day before it changes its 
skin, as in the male Ephemerus, or the Fly 
thence produced after changing its coat. Thefe 
fpermatic veflels are found to be placed on each 
fide of the ftomach and inteftines, and appear 
like the {mall guts in Fifth. There are, how- 
ever, fome bendings and windings in them, 
like the feminal veficles in the human {pecies 
and they are found in manner of tubes: there- 
fore, in this refpeét, they are alfo analogous 
to the fpermatic veffels of fome quadrupedes, 
as Moles, Hedge-hogs, and the like. They 
are in thefe, Worms of an oblong figure f/f, 
and are extended all over the belly, as is evi- 
dent from the annexed figure, wherein I ex- 
hibit one of them taken out of the body, and 
the other fomewhat larger than nature in it, 
They contain in their cavities a very white 
humour like milk, which is the fperm. The 
feminal veffels themfelves are likewife perfectly 
white, and they are of a thin and membranous 
texture, and have many air-tubes all over them 
both within and without. 
Er? 
ofiN, AB UR HE 
of, 
In the lower rings of the abdomen appear 
two other little parts dd, which likewife in 
my opinion belong to the f{permatic vefiels ; 
for they feem to have a common paflage with 
them and with the inteftines, Tab. XIV. fig. 
1. ¢; which however I could not at that time 
fo accurately difcover, being engaged in other 
parts of this diffe€tion. And indeed we mutt 
diffect a great number of thefe infects, if we 
would endeavour to difcover the whole fabrick, 
fearching in another what we could not ex- 
amine to our wifhes in the former; and even 
with this caution we cannot always execute 
our defign perfectly. 
The ovary is double in the females, Tab. 
XV. fig. m1. and it is placed im the’ fame 
manner as the ovary in Fithes. But if the skin 
of the abdomen be opened a little way with a 
fine and fharp-pointed pair of f{ciffors, that con- 
geries or heap of eggs, fig. 1. //, fituated on 
each fide of the foft part of the belly, comes 
in fight. Between thefe, in the middle, the 
ftomach and inteftines ff are fomewhat ob- 
fcurely feen through the other parts, and the 
latter are themfelves ftrongly connected with 
the membranes mm of the ovary. ‘The fto- 
mach and little inteftines appear the more 
plainly, the more they are filled with mud, 
which is the food of the Ephemerus ; and for 
this very reafon the eggs may be feen alfo more 
beautifully ; for their whitenefs, fhewing itfelf 
brighter on account of the diverfity of colours, 
makes them the more difcernable. 
The double ovary of the Ephemerus has in- 
numerable air-pipes, which are tied to a {mall 
membrane that furrounds the ovary; and by 
means of the latter they are conveyed to the 
little eggs hidden on the infide. But if this 
membrane be removed with the point of a fine 
needle, and fome part thereof put together 
with the eggs into a fpoonful of water, the 
eges immediately feparate from each other, 
and there remains a fine, delicate and tender 
bundle of minute veffels, fig. vir. g, which I 
take to be moftly air-pipes, being like fine fila- 
ments, and confpicuous by their colour like 
mother of pearl. 
The eggs are likewife fo extremely {mall, 
fig. 11, that they can fearce be feen. It is there- 
fore neceflary to view them with a good mi- 
crofcope, and to put them on black or blue 
paper, which contributes to their being the 
better diftinguifhed. 
The eggs are of a plain round and oblong 
figure, and are furrounded with a tolerable 
firm membrane, which appears cloudy under 
the microfcope, and they are of a white colour, 
like the inner skin of an egg-fhell. Since 
therefore the eggs of the Ephemerus are fo 
fmall and delicate, the reafon is evident, why 
the Worms iffuing from them muft be in- 
creafing three years before they come to per- 
feGtion, and are able to commence their 
change. 
CE aa; 
