MICROSCOPIC OBJECTS. 123 



small Crustacea, the circulating fluid traverses the limbs, 

 antennae, and tail, and thence moves along- the dorsal 

 vessel towards the head and down the sides of the body- 

 in cavities and not distinct vessels, hence called diffused 

 circulation. Tlie most favourable subjects for viewing 

 this are the following, the first six of which are drawp 

 and described in the ' Microscopic Illustrations' and 

 'Cabinet': — Larva of the Ephemera — (The recent 

 discovery of the beautiful mechanism of the dorsal vessel 

 of this larva by Mr. Bowerbank is fully conjBrmed by the 

 careful dissections of Mr. Newport, who with much 

 perseverance has extended these inquiries to the other 

 states of insects ;) — Larva of Hydrophilus ; small Dytiscus ; 

 Agrion Puella — (In this elegant larva I have not observed 

 the circulation in the legs to extend beyond the haunches ;) 

 LibeUula ; round Lynceus ; freshwater Shrimp ; Water- 

 hog (Oniscus) ; Ligia; WditeY-Resx (Dajjhnia Puleo!), &c. 

 Power 100 to 300 times. In several of the Polj^iferous 

 Zoophytes, as the Tubularia indivisa, Sertulariee, Campanu- 

 larise, Plumulariee, &c., Mr. Lister has by means of the 

 achromatic engiscope discovered a circulation to exist 

 which in many respects resembles that in plants. 



' ' Tlie circulation in plants termed cydosis is a revolution 

 of the fluid contained in each cellule, and is distinct from 

 those surrounding it. It can be obser-ved in all plants in 

 which the circulating fluid contains particles of a diflerent 

 refractive power or intensity, and the cellules are of suffi- 

 cient size and transparency. Hence all lactescent plants, 

 or those having, a milky juice, with the other conditions. 



