ACANTHOCEPHALA CLASSIFICATION 



181 



Fig. 99. A, The larva of Echinorhynchus proteus 

 from the body-cavity of Phoxinus laevis, with 

 the proboscis retracted and the whole still 

 enclosed in a capsule. B, A section through 

 the same ; a, the invaginated proboscis ; b, 

 proboscis sheath ; c, beginning of the neck ; 

 d, lemniscus. Highly magnified. (Both from 

 Hamann.) 



are ten of these, but the number is not the same in all species. 

 The syncytium is in a fluid state, with a few gigantic nuclei 

 floating in it ; these now lose their spherical shape, and throwing 

 out processes become amoe- 

 boid ; in this way they bud 

 off small portions of their 

 substance, and from these 

 the oval nuclei of the sub- 

 cuticle and the lemnisci 

 arise. The rest of the syn- 

 cytium hardens into the 

 fibrillar matrix of the 

 sub -cuticle, leaving, how- 

 ever, scattered spaces which 

 form the sub - cuticular 

 sinuses of the adult. An 

 interesting feature of N. 

 clavaeceps and Arhynchus 

 hcmignathi is that the skin of the adult retains the larval 

 features, and it and the lemnisci consist of a syncytium with a 

 very few giant nuclei scattered through it. Hamann counted 

 only eight in the skin and two in each lemniscus in the example 

 figured on p. 178. 



The whole of the rest of the body is formed by the entoblast. 

 Within the latter a circular split arises which separates a single 

 layer of outermost cells from an axial strand of many cells (Fig. 

 98, B). The split is the future body-cavity; the axial strand 

 forms the proboscis, its sheath, the cerebral ganglion, muscles, etc., 

 and the ligament with the contained generative organs ; the 

 outermost layer of cells forms the muscular lining to the skin. 

 It is interesting: to note that these cells destined to become 

 muscle-fibres are at first arranged as a single layer of cubical 

 epithelial cells lining the body-cavity ; most of them become 

 circular muscle-fibres, but a few are pushed inwards so as to 

 lie next the body -cavity, and these become the longitudinal 

 fibres. 



Classification. Until recently the Acanthocephala were 

 supposed to include but one genus, Echinorhynchus, with several 

 hundred species, but Hamann 1 has pointed out that these species 

 1 Zool. Anz. Bd. xv. 1892, p. 195. 



