Invertebrate Gallery of the Indian Museum. 109 



In cases where the ambulacra are reduced to three^ 

 these are commonly placed close together on one face of 

 the body, which then becomes a flattened ventral surface or 

 "foot'", upon which the animal progresses like a snail or 

 slug, while the opposite surface becomes a strongly convex 

 back. This is excellently shown in the specimens of Mul- 

 leria miliaris in Case 36, which have a strong resemblance 

 to a slug. In the beautiful specimens of Deima this modi- 

 fication of the form of the body, showing a flat ventral sur- 

 face, or " foot ", for progression, and a convex hogged back, 

 is even better marked ; but in Deima instead of three ven- 

 tral ambulacra there are only two. 



The external characters of the typical Holothurian are 

 conspicuously easy to note. The body is elongate and more 

 or less cylindrical, tapering at both ends. At one end 

 (oral pole) we find a large mouth surrounded by a crown of 

 tentacles, which last, however, are very commonly retracted 

 within the mouth. At the opposite end (anal pole) is seen 

 the anus, which is often surrounded with a ring of more or 

 less calcareous papillae, or " teeth". 



The details of the internal structure of the Holothuroi' 

 dea — the digestive system, the internal respiratory system, 

 the water-vascular system, the generative system, etc. — 

 are very clearly shown in the series of dissections in spirit 

 of Holothuria^ StichopuSy and Mulleria^ in Case 36. The 

 dissected specimens of Stichopus and Mulleria exhibit 

 very beautifully a curious feature in the life of these ani- 

 mals: in the Stichopus the body-cavity is seen to be occu- 

 pied by a long eel-like fish of the genus Fierasfer, the head 

 of which lies in the cloaca of the Stichopus : in the Mulleria 

 the cloaca is occupied by a small crab. At first sight it 

 might appear as if the fish and the crab were parasites upon 

 the animal in which they are found, and lived at the ex- 

 pense of their host ; but that this is not so is proved by the 

 fact that both the fish and the crab have all their organs of 

 nutrition, respiration, circulation, excretion, locomotion, 

 volition, etc., fully and perfectly developed, — a state of 



