LESSON 32.] NUTRITION IN THE ECHINODEKMA. 



115 



FIG. 192. 



545. From the amazing number of ova deposited by the various 

 species of Holothuria during only one season, they ought to be the 

 most abundant of all animals, instead of being moderately rare ; the 

 probability is that their eggs are greedily eaten by -small fishes, Me- 

 dusae, some Zoophytes, and, in fine, by the host of small Carnivora 

 incident to the ocean. 



A preparation of the Ovarium of Cucumaria frondosa, dissected 

 out of the body, is shown in Fig. 192. The tubuli are suspended by 



the oviduct (a), the tubes 

 being quite full of ova, of a 

 rich orange color. The organs 

 of reproduction are placed in 

 the head, between the ten- 

 tacula; the external orifice 

 of the oviduct is a small, dark- 

 colored papilla, which (unless 

 carefully sought for) might 



FIG. 193. 



Ovarium, Cucumaria frondosa. Enlarged ovarian tubuli, C. frondosa. 



easily elude detection. An enlarged view of these ovarian tubuli, 

 showing their contents, is given in Fig. 193. 



546. One of the most elegant preparations the animal kingdom 

 can furnish, is the respiratory organs of Holothuria. 



Those of Cucumaria frondosa are reduced from eleven inches in 

 height, and shown in Fig. 194. The cloaca (a) is entirely covered 

 with strong, flat muscles, which were attached to the muscular coat 

 of the integument. Great muscular power is necessary to this organ, 

 whose constant function it is to draw water from the ocean, pump it 

 up to the minutest sac, or modified air cell (d), and discharge it 

 when unfitted for further use. Beside the Cloacal outlet, there must 

 be a series of minute apertures, which have hitherto defied discovery 

 in connecting with this apparatus, for, if a specimen (previously ac- 

 customed to handling, by being tickled daily, in sea water) be care- 



