96 STEKELMIXTHA. 



and lodged in a depression formed by the inversion of the in- 

 tegument, so as completely to hide it within the body. This 

 inversion is produced by the contraction of two muscular bands, 

 (d, e,)* which arise from the inner walls of the body, and are 

 inserted into the root of the proboscis around the oesophagus : 

 two other muscles, (6, 6,) antagonists to the former, arise near 

 the spines themselves ; and these, aided by the contractions of 

 the walls of the body, are the agents by which the protrusion 

 of the head is effected. Although the teeth or spines, which 

 render this organ so formidable, are merely epidermic appendages, 

 they are found to be rendered erect or depressed at the will 

 of the creature ; and it is therefore probable that, minute as they 

 are, they have muscular fibres connected with them serving 

 for their independent motions : these spines, moreover, are not 

 always confined to the head ; but in many intestinal worms are 

 found on various parts of the body, wherever their office as 

 instruments of attachment is by circumstances rendered needful. 



(127.) The digestive system of the Echinorynchus is extremely 

 simple. The mouth is a minute pore placed at the extremity of the 

 proboscis, which communicates with two slender canals, (f,f,) at 

 first of great tenuity, but towards the middle of the body assum- 

 ing something of a sacculated appearance. Towards the tail 

 these vessels gradually diminish in size until they are no longer 

 distinguishable ; but they have not been seen to give off any 

 branches, or to communicate with each other. 



Near the origin of these nutrient tubes are two large caeca, nearly 

 an inch in length, called lemnisci, (fig. 41, 1 and 2, d, d,) which 

 are probably connected with the digestive function. 



(128.) The female Echinorynchus is, as is usually the case in 

 Dioecious Entozoa, considerably larger than the male, as may be 

 seen in the figure. In the former (fig- 41, 1) the ovary (c) is a 

 capacious organ occupying the centre of the body, and extending 

 along its entire length. When minutely examined, it is found to 

 consist of two compartments or distinct sacs, one occupying the 

 dorsal, the other the ventral aspect ; the two tubes being separated 

 by a septum. The dorsal ovary commences near the tail, at g, by 

 a cul-de-sac ; and, enlarging as it runs forward, terminates near the 

 point c, by uniting with the ventral portion. The anterior part 

 of the canal (b) is common to both divisions of the ovary ; and 

 from this the ventral tube runs backwards to the posterior end of 



* These muscles are seen of their natural size in fig. 1 at e, e. 



