EXPLANATION OF THE PLATES. 



I am indebted to Professor Moseley for the drawings of Hypobijtlt'ws cahjiixlrs, from 

 which figures 1, 2 and 5 on Plate XXXVII. have been prepared. Figure 1 on Plate 

 XVIII. is taken from a careful drawing executed for Mr. Murray by Mr. George West. 



With the exception of these four, all the figures have been lit In >u iaj >li< -< 1 by .Mr. 

 Frederick Huth, jun., from my own drawings, supplemented, in the case of a few of the 

 views of the external appearance, by the actual specimen represented. 



It may be well to mention that some of the branchial sacs represented are " combina- 

 tion figures," formed of small portions from several different specimens pieced together. 

 It was necessary to adopt this plan, in order to show the various important points of 

 structure within the compass of a reasonably small figure. 



With the exception of a few which are only slightly enlarged, all the magnified 

 figures were drawn as seen by one of the following combinations, and are marked in the 

 explanations with the number of the objective used : — 



Hartnack, obj. 4, with medium ocular 

 Hartnack, obj. 5. ,, ,, 



Hartnack, obj. 7, ,, ,, 



Hartnack, obj. 10 (water immersion), 

 Zeiss, obj. T V (oil immersion), with ocular 4 



x 50 

 x 180 

 x 330 

 x 750 

 x 950 



LIST OF ABBREVIATIONS. 



the capillaries. 



the central brown area in the endo- 



style. 

 the connecting duct in the bran hial 



sac. 

 the dorsal lamina. 

 the dorsal tubercle, 

 the external longitudinal vessels in 



the branchial sac. 

 the end style, 

 fibres in the test, 

 the hermaphrodite genital mass. 

 R 39 



