Animalcules 'with Shells and TV he els. 299 
celved in this, having a regular Syftole and 
Diaftole, and nearly of the fame Form and 
Size with the Heart of the common Wheeler , 
as the Figures 7, 8, and 9, are intended to 
fhew at the Place marked a. 
This Species likewife draws its Head and 
Tail occafionally within the Shell, as a tfig m 
1 o and then its Shell appears terminated 
on its Fore-part by fix fhort Spikes on one 
Side of the Rim and two on the other, in- 
Read of the four long ones wherewith the 
firfh Sort is armed : but this does not always 
protrude its Head like the other, fo far out 
as to cover the Edges of the Shell intirely: 
fometimes on, the contrary, the Spikes of the- 
Shell are feen beyond the Head, and the 
Fibrillce mentioned in the former Defcrip- 
tion appear playing between them, as at Jig , 
7. However the Head very commonly is 
as at the Figures 8 and 9.-Thefe are the 
chief Particulars wherein this Animal differs 
from the former. 
As to their Propagation, both Species car¬ 
ry their Toung in oval Sacculi or Integu¬ 
ments, fattened, externally, to the lower Part 
of their Shells fomewhere about the Tail: 
Thefe Sacculi are fometimes opake only at 
one End, and feemingly empty at the other, 
fee Jig. 5 : Sometimes the Middle Part ap¬ 
pears opake with a Tranfparency all round, 
like Jig. 7 ; and much Variety of Darknefs 
and Tranfparency may be diftinguifhed, ac¬ 
cording 
