14 



LUCERNAKI^ AND THEIR ALLIES. 



31. The interior configuration (PI. mjo- ^'>) corresponds, in a general sense, with 

 that of the exterior. The proboscis (p) forms the boundary of a similarly shaped 

 space, and thence the passage is direct into a very wide quadripartite area ((j^) 

 which is coextensive with tlie depth and width of the umbella. The umbellar 

 area (iV) narrows posteriorly into a broadly conical outline (u"), and then opens into 

 four circumaxial, elongate, tuimel-likc passages (t'), which extend to the posterior 

 end of the caudal region. Essentially, therefore, the whole internal cavity consti- 

 tutes one common chamber, \vhich is subdivided in accordance with the configura- 

 tion of the three principal regions of the body. 



32. Habitat. — Although a free, single, independent body, ITallcJystus aurmila is 

 eminently sedentary in its habits, and even is partially encased in a very short 

 sheath at its posterior attacliment, so that it has the appearance of being a perma- 

 nently adherent l)ydroid, like Coryraorpha, Hybocodon, etc., and in fact it is very 

 rare to find it disengaged from its caudal mooring, when in its natural habitat. 

 Wlien, however, it is transported, with the eel-grass to which it is most commoidy 

 attached, it very often loosens its hold, slips out of its sheath, and moves about from 

 place to place in its temporary abode As it is very difficult to keep it in a healthy 

 condition, requiring a large amount of water, frequently to be renewed more- 

 over, its habits, attitudes, configuration, and even general structure need to be 

 observed as soon as possible after it is removed from its natural resting place, and 

 if practicable, as we have often found it, even before this is done. T'he numerous 

 figures (.A'.ys. 1-1 G) wliich we have placed on the plate (PI. i) were drawn from life 

 wliile tlie subjects were under tlie most favorable conditions, and are, therefore, fair 

 samples of the natural attitudes and habits of this species. 



33. As we have said above, it is most frequently found attached by its caudal 

 extremity either to eel-grass (Zostera), or to the common Fuciis vesicnlosus, and 

 very rarely to the solid rock. It would seem to prefer for its base of operations 

 some object which is kept in constant motion by the action of the water, something 

 which will assist it in coming in contact with the greatest possible amount of respi- 

 ratory material. Hence we may account for the difficulty of keeping the animal 

 ni a healthy state in confinement. It will appear, to the inexperienced eye, to be 

 perfectly well and fully expanded for three, four, or five days after capture, but 

 during all this time it is quietly exfoliating its epidermis, both externally and 

 internally, and finally indicates its illness, in its extreme, by foiling from its 

 attachment, and lying inactive at the bottom of the aquarium, contracted and rolled 

 rip into an almost shapeless mass. Such has been our. experience whenever we 

 ceased from making the utmost efforts to keep the animal supplied with an abun- 

 dance of perfectly fresh and cool water. We have seen statements that it thrives 

 well m an aquarium; but we are fully persuaded that it was only apparently so, 

 and that, after the first forty-eight hours of confinement, it was unfit for anatomical 

 investigation, certainly of a histological character. 



34 Attitudes —The principal attitudes of the body may be reduced to two in 

 number; the one most common is wlien the umbelliform portion is more or less 

 concave anteriorly (fig. 5), so that the proboscis is, as it were, surrounded by a very 



