AT THE MICROSCOPE. 47 



EXPLANATION OF PLATES XXL, XXIL, XXIIL, 

 XXIV., XXV. 



Plate XXL 



Fig. L — Represents one of the young specimens of Polystomella : the 

 dotted lines show the probable length of the sj)ines in their 

 perfect condition. 



,, 2. — A mature example. 



,, 3. — Periphero-lateral aspect of the same after Williamson: s._p., 

 septal plane ; s.o., septal orifice. The above are magnified 

 50 diameters. 



,, 4. — Lateral aspect of P. umhilicatula. 



,, 5. — Periphero-lateral asjDect of the same after Williamson. 



,5 6. — Antennae of Sijrphus. 1. — The Basal. 2. — The Second. 

 3. — The greatly enlarged and club-shaped Third joint. 

 4. — The plumose setae. 



,, 7. — Ovipositor of Saw-Fly as seen with a low power. The num- 

 bers indicate those of the abdominal segments. 7, 8, and 9, 

 show the possession of sx)iracles, x 5 diam. 



,, 8. — The saws, with the saw-hooks, x 50 diam. 



,, 9. — One of the saw-teeth x 200 diam. 



Plate XXIL 

 Fig. 1. — Flea from cat, ^ , x 30 diam. The numbers, 1, 2, 3, etc. , 

 indicate the number of the segments, 2 being the pro-, 3 the 

 meso-, and 4 the meta-thorax. On the 12th dorsal segment 

 two long, stout setcie are seen. X, a scale attached to the 

 meso-thorax, representing an anterior wing ; X, X, a larger 

 scale connected with the meta-thorax, partly overlapping the 

 dorsal portion of the 5th seguient, representing a rudimentary 

 posterior wing. 



-The Tongue (" lingua "). 



-Meta-thoracic spiracle of the left side. 



-Digestive organs of Blow-Fly, after R. B. Lowne. 



-The object on slide " Stomach of Blow-Fly " as viewed with 

 a low power. 



Plate XXIIL 

 -Sting of Sand-Wasp x 25 diameters. 

 -The barbs with their sheath x 150 diameters. 

 -The barbs and end of sheath of the sting of Common Wasp 



X 150 diam. , for comparison. 

 -Spiracle of Ammophila. 

 -Acarus from Finch, Dermaleichus passerinus (Koch), Acarus 



chelopus (Hermann) ^ , Dorsal aspect, x 100 diameters. 



