114 ANIMAL PHYSIOLOGY. [LESSON 32. 



until it terminates in the cloaca,// it is connected to the body in 

 several places by a mesentery of great vascularity (e, e), which also 

 connects one fold of the intestine to another. 



539. The branchise (gills, h), which arise from the cloaca, give 

 off a great number of ramified branches from the central stem. 

 They are always filled with sea water, from which the gills possess 

 the power of eliminating the oxygen ; the vesicles, or cells of the 

 gills, are described at m. The blood-vessels which pass from the 

 mesentery to the gills, conveying the blood to be aerated, are shown at 

 n / and the external opening of the cloaca at g. 



Seen in a recently killed specimen, these gills form a very inter- 

 esting object ; they then seem to exhibit a constant vermiform mo- 

 tion, which continues long after the apparent death of the animal. 



540. One fact in connection with Holothuria is too remarkable 

 to omit. Those persons who handle a living specimen for the first 

 time, will be surprised to find that, without the slightest provocation, 

 the integument suddenly bursts, and the whole contents of the body 

 are violently thrown out ; neither is this all, for, if the emptied skin 

 be thrown into a vessel of sea water (which should be renewed da'ly), 

 the alimentary canal, and all the lost organs including the teeth 

 and the tentacles will be reproduced. 



541. This act appears to be due to the excessive irritability of 

 these animals, which, when once excited, appears to be beyond its 

 power to control. The muscular system is of enormous power, es- 

 pecially in the transverse direction of the body. 



542. To enable the creature to shorten its length, and to retract 

 the head, strong tendinous chords are attached to the muscular coat ; 

 of these, five are devoted to the head alone. 



543. The Cucumaria frondosa is the reputed largest Holothuria 

 known ; Fig. 190 is copied from a specimen, now in the Hunterian 

 Collection, England, which measures twelve inches in the dead state ; 

 beside it, in the Museum, is a preparation of another individual of 

 the same species, which, in life (sometimes) measured three feet 

 it did so at the moment it was killed, and at the instant contracted 

 to four inches, all that it measures now. 



544. The sexes in these animals are separate ; the important 

 organs of the female the tubuli containing an immense quantity of 

 ova are seen at k. These, filled to repletion with their valuable 

 contents, form a very interesting object for the microscope, while the 

 rich orange color of the ova contributes greatly to the attractiveness 

 of such a preparation as that figured. 



