212 Transactions of the 



this purpose without iuvolving any measurement whatever, when it 

 only requires the operator to Jill in at his discretion their respective 

 varying outliaes. And here the shifting stock of the T square 

 comes to our assistance. 



The varying proportions of the pellets in the tapering portion 

 of the tube would at a glance seem to impose the necessity for a 

 tedious repetition of all the foregoing operations ; but nil despe- 

 randum, the central positions of any two pellets in their peculiar 

 disposition are precisely equidistant from their neighbours right 

 and left, as they also are from each other vertically, or would be so 

 on a plane surface, the difference due to the circular outline of the 

 tube being in this instance inappreciable, so that the centres of 

 the vertical and horizontal courses of the pellets form together a 

 double series of eqmlateral triangles all down the tube, whether 

 parallel or tapering, and by the employment of ihe set-square of 

 '6(f we obtain their correct central positions and resulting diameters 

 all down the whole length of the tube, thus determining the data 

 from which all the others have to be projected and set off more 

 accurately than could be attained by any method of scaling. 



The projection of the trochal disk embracing the four frontal 

 lobes "with their marginal ciha and supporting ligaments, the 

 secondary range of decumbent ciha terminating in the pellet cup 

 beneath the dorsal lobe, and the two conspicuous antennae though 

 less comphcated, necessitate an equally careful apphcation of this 

 system, especially where, as in this particular instance, it is intended 

 to show the animal at the same inclination as its investing tube, and 

 inclined also in its horizontal position, so as to relieve it of the too 

 formal and diagramatic character imposed by parallelism, and hav- 

 ing selected such an attitude, the several diagrams which have been 

 constructed from actual measurements, are arranged in the several 

 positions shown in Plate LXXXIII., which are necessary to produce 

 the finished form ; Fig. 9 being a dorsal view, Fig. 10 a plan of the 

 superior lobes, Fig. 11a plan of the inferior lobes, and Fig. 12 a 

 lateral view ; and it only requires the several intersections of the 

 coincident points from the different views to be foUowed, to trace 

 the outhne and prominent featui-es in Fig. 13, which is a rough 

 outline of the finished drawing, Plate LXXXIV. 



Eeeata in last Paper. 



Owing to certain exigencies which obstructed the proper correction 

 of the proofs of ray pajjer " Ou the Winter Habits of the Rotatoria," 

 I desire here to explain that page 1G8 line 10 from the bottom shoixld 

 read Clustered Free; and line 4 on page 1G9; by means of the 

 currents it creates. 



