LUCERNARIvE AND THEIR ALLIES. 17 



It will on this account be more readily understood if we indicate, with a few li<'lit 

 touches, the configuration of the anterior foce of the umbel. This face is sub- 

 divided into eight alternately sunken and elevated regions, so placed that the 

 sunken areas {figs. 22, 37, ^-) abut against the four sides of the proboscis, and the 

 elevated fields are continuous with the corners (^') of the latter. The sides of the 

 proboscis, it will be seen now, extend much further backward than the buttress-like 

 corners ; the former trending parallclwise with the axis of the body until they 

 reach the uttermost depths of the umbellar concavity (at p', fig. 37), gradually 

 narroAvas they approach the bottom of the U-slifiped sunken areas, and meanwhile 

 insensibly shade off, laterally, into the gradually and consentaneously widening 

 ])roboscidial buttresses (^'); while the latter rapidly rise from the adjacent hollows, 

 and shade off with a very gentle slant into the corresponding elevated regions of 

 the umbel. Tlie latter regions, therefore, lie, respectively, two in the horizontal 

 axial plane, and two in the vertical plane, while the sunken areas trend each at an 

 angle of forty-five degrees to these planes. 



40. The flat sides of the proboscis do not by any means always stretch with a 

 straight, smooth surface in a direct line away from the mouth, but rather, and most 

 frequently, they are transversely wrinkled, and often deeply folded in the same 

 direction; and to such an extent, sometimes, do these folds reach that they cover 

 over a considerable portion of the deeper, proximal ends of the sunken areas, and 

 form thereby a sort of marsiqnnm or pouch {fig. 22, 2,~). These folds evidently 

 possess a high degree of contractility and expansibility, as they may either be ex- 

 tended so as to reach at least half way to the margin of the umbel, or they may be 

 so retracted that the sides of the proboscis are perfectly smooth, as may be seen on 

 its upper right side in fig. 22. The extensibility as well as the strength of the 

 proboscis may be observed also when it seizes and swallows a shrimp of compara- 

 tively large size. Tlie marginal adherent organs (a) are on such occasions of 

 eminent service, while the tentacles are occupied in thrusting the victim into the 

 widely spread mouth, whence it passes through the proboscis, Avhicli fulfils merely 

 the office of a throat, to the general cavity. 



§ 8. T7w Umhella. (PI. i,figs. 2, 3, 17; PI. n.fig. 22; PI. m.fiig. 37; 

 PI. iY,fig. 47 ; PI. \i, fiigs. 61, 62, 66.) 



41. The Umhella. — We shall next consider the form, proportion, appendages, 

 contents, and general and special morphological relations of the middle division of 

 the body. The umbella presents an outline which varies to a considerable extent 

 with the shifting moods and attitudes of the animal. In profile it is concave in 

 front and convex behind [figs. 17, 37), the concavity holding the proboscis in the 

 middle, and the convexity abruptly narrowing off at its axis, into the pediuicular, 

 caudal termination (t). Viewed from the front {figs. 2, 3, 22), it presents an 

 octolateral outline, with eight strongly projecting corners. Of these eight sides 

 four alternate ones are usually shorter than the others, and they are those which 

 lie directly opposite the four flanks of the proboscis {figs. 2, 22, 37). Frequently, 

 however, the proportions are reversed and the longer four become the shorter ones 



3 February, 1877. 



