ANNULOIDA: SCOLECIDA. 17S 



developed in a manner closely analogous to that described as 

 characteristic of the Echinodermata. The larval form of Ne- 

 mertes was described by Johannes Muller, under the name of 

 Pilidium (fig. 50, 4). It is " a small hemet -shaped larva, with 

 a long flagellum attached like a plumelto the summit of the 

 helmet, the edges and side-lobes of which are richly ciliated. 

 A simple alimentary canal opens upon the under surface of 

 the body between the lobes. In this condition the larva 

 swims about freely; but, after a while, a mass of formative 

 matter appears on one side of the alimentary canal, and, elon- 

 gating gradually, takes on a worm-like figure. Eventually it 

 grows round the alimentary canal, and, appropriating it, de- 

 taches itself from the Pilidium as a Nemertid — provided with 

 the characteristic proboscis, and the other organs of that group 

 of Turbellaria." — (Huxley.) 



CHAPTER XXVI. 



NEMATELMIA. 



I. ACANTHOCEPHALA. 2. GORDIACEA. 3. NeMATODA. 



Division II. Nematelmia. — This section may be considered 

 as comprising those Scolecids in which the body has an elon- 

 gated and cylindrical shape. Strictly speaking, it should 

 include the Nemertida, but the division is not founded upon 

 anatomical characters, and is employed here simply for con- 

 venience. Most of the Nematelmia possess an annulated in- 

 tegument; but there is no true segmentation, and there are 

 rarely any locomotive appendages attached to the body. The 

 majority are unisexual, and parasitic during the whole or 

 a part of their existence. Three orders are comprised in 

 this division — viz., the Acanthocephala, the Gordiacea, and the 

 Nematoda. 



Order I. Acanthocephala. — The Acanthocephala are en- 

 tirely parasitic, vermiform in shape, and devoid of any mouth 

 or alimentary canal. They are provided with a kind of snout 

 or proboscis armed with recurved hooks, which is continued 

 backwards into a bandlike structure (ligamentum suspensorium), 

 to which the reproductive organs are attached. " Immediately 

 beneath the integument lies a series of reticulated canais con- 

 taining a clear fluid, and it is difficult to see with what these 



