540 R. T. GUNTHER. 



less well euough preserved for the elucidation of many struc- 

 tural points. All my observations are based on sections cut 

 by the ordinary paraffin method and stained in various ways, 

 but those which had been coloured with Kleinenberg's haema- 

 toxylin gave as satisfactory results as any. Notwithstanding 

 the age of the material, I have been able to confirm most of 

 the observations of AUman and Lankester (2 and 4), and to 

 add some further details regarding the structure of the ten- 

 tacles, the sense-organs, and the male reproductive organs. 



The general proportions of the various parts of the body as 

 seen in meridional section are shown in PI. 40, fig. 1. In the 

 section of the individual there figured the mouth of the bell is 

 considerably contracted, so that the manubrium is enclosed in 

 the subumbrellar cavity ; but in the living condition, when the 

 animal is fioating in the water, the bell has a much more 

 flattened shape, and the manubrium then projects considerably 

 beyond the margin of the umbrella. The mesogloea of the 

 umbrella is fairly uniform in thickness throughout, being only 

 very slightly thicker in the centre than near the circular canal. 

 In the manubrium, however, the mesogloea is not so evenly 

 distributed, but is thickest at the distal end of that organ, the 

 proximal end being almost completely destitute of any gela- 

 tinous middle layer whatever. This distribution of the meso- 

 gloea may be in relation to the great extensibility of the 

 manubrium. It is probable that the extension of that organ 

 is chiefly effected by the elongation of its proximal end, and 

 that a well-developed muscular layer exists between the limit- 

 ing epithelia of this region. 



In none of the preceding papers are the figures of the 

 arrangement of the organs situated at the margin of the 

 umbrella satisfactory, while that of the "diagrammatic 

 meridional section " of Allman (4, p. 132) is erroneous and 

 misleading. The relations of the organs situated round the 

 periphery of the umbrella are exhibited in transverse section 

 in PI. 40, figs. 2 and 3. Fig. 2 is a section passing along a 

 radial canal (r. c.) and through the base of a radial tentacle 

 {te.), while fig. 3 is taken several sections further on, passing 



