76 EDGAR J. ALLEN. 



which the objects must remain iu the solution varies from 

 three to twelve or fourteen hours, according to the degree of 

 softness of the chitiu. Animals which have recently moulted 

 have their gills well preserved in about three hours. The 

 best average time is from five to six hours. After being 

 hardened in alcohol the objects were stained with Delafield's 

 hsematoxylin ; or they were removed from Flemming's solu- 

 tion to water, and, after a few minutes, transferred to crude 

 pyroligueous acid, where they remained for nearly twenty- 

 four hours. By this process the osmic acid is reduced in the 

 tissue, and no further staining is required (von Mahrenthal's 

 method). This latter method is the one which has been 

 chiefly used. After dehydration the objects were sunk in 

 chloroform, and then placed for several hours on the water- 

 bath in a mixture of chloroform and paraffin. They were then 

 embedded in paraffin and cut in the usual way. 



Arrangement of the Gills. — The arrangement of the 

 phyllobranchiate gills of Palsemon has been described by 

 Huxley/ and P. Mayer^ has shown that Huxley's description 

 is also true for Palsemonetes varians. The second maxil- 

 lipede bears a podobrauchia, the third two arthrobranchise, 

 and there is a pleurobranchia above each of the five walk- 

 ing legs. 



Structure of the Gills. — Each gill consists of a vertical 

 axis, bearing on its external surface two rows of lamellae, each 

 lamella sloping relatively to the axis forwards, upwards, and 

 outwards, making an angle of about thirty degrees with the 

 horizontal. The gills above the thoracic legs taper towards 

 their two ends, the lower ends, however, being less sharply 

 pointed than the upper. The gill above the third walking 

 leg is attached to the body at about the middle point of its 

 axis. Those in front of the third leg are attached slightly 

 above, those behind slightly below the middle points of 

 their axes. 



^ " On the Classification and Distribution of the Craylishes," ' Proc. Zool. 

 Soc.,' London, 1878. 

 ' •• Carcinol. Mitt.," ' Alitt. a. d. Zool. Sta. iu Neapel,' J3d. ii, 1881. 



