Cuvierian Organs o/'llolotliuria ni^i^ra. 279 



muscles, which tend by their contractioa to curl up the cut 

 integument and pull out t!ie pins. When the muscles were 

 thus stupefied the dissection was carefully proceeded with, 

 and wlu'n finished placed in stron<»- spirit. In this manner 

 the result was obtained shown on Plate XVII. fig. 9. The 

 Cuvierian organs [c.o.) are seen lying in a great mass 

 attached to the left respiratory tree {l.rsp.). Some of them 

 (coJ) have detached themselves from the main body and 

 have passed through an opening in the dorsal wall of the 

 clonca and out through the anus to the exterior. 



To confirm the results so obtained I employed another 

 method. In the store of the Marine Biological Association 

 there were a great number of specimens of Holothuna nigra 

 preserved in spirit, many of which had in dying partially 

 ejected their Cuvierian organs and were to be seen with a 

 bunch of these organs protruding from the anus. Selecting 

 such a specimen, I cut a series of thick sections through the 

 cloacal region with the hand, using a sharp razor and 

 arranging the sections in order. 1 obtained nine such sec- 

 tions through the cloaca and the base of the respiratory trees, 

 and in figs. 2-8 on Plate XVII. seven of them are diagram- 

 matically represented. 



In the first section (fig. 2) the cloaca (cL) is seen filled with 

 Cuvierian organs {c.u.) and attached to the body-wall [int.) 

 by radiating muscles. The five longitudinal muscles are just 

 visible. The third and fourth sections (figs. 3 and 4) are 

 similar but larger, and the number of Cuvierian organs is 

 greater. In the fifth section (fig. 5) the Cuvierian organs 

 are now close up against the dorsal wall of the cloaca; a few 

 appear also entangled in the cloaeal muscles to the left and 

 venirally. In the sixth section (fig. 6) the wall of the cloaca 

 is wanting on the dorsal side, and the gap is filled by 

 Cuvierian organs which are oval in section, showing that 

 they are cut obli(i[uely and are hence passing downwards and 

 backwards. The seventh section (tig. 7) passes through the 

 S|;ot where the cloaca gives off a brancli, the left respiratory 

 tree [l.rsp.), to which the Cuvierian organs are beginning 

 to be attached. It is notert-orthy that dorsally some of the 

 Cuvierian organs are cut twice in the section, and can be seen 

 in fact to ber.d backwards, curving slightly to the right. lu 

 the eighth section (lig. 8) tlie res[)iratory tree is quite 

 distinct from the rectum, which is placed more ventrally and 

 attached by a mesentery between the median and right ventral 

 longitudinal muscles. A great number of Cuvierian organs 

 are attached to the respiratory tree, and a similar curving 

 back can be observed in some of them to that pointed out in 



