INTESTINAL WORMS. 169 



joint, yet nearer the anterior edge, with two openings : through the 

 anterior and larger the penis is evolved; the posterior smaller 

 is the female sexual opening: round both of them are minute 

 white points which EscHRiCHT 1 concluded, under high powers of 

 the microscope, to be follicles (mucous crypts of the skin). The 

 eggs of BotJiriocephalus have a hard shell, as in the Distomes, of a 

 brown or brownish-yellow colour, and seem like them to spring 

 open with a sort of hood. In the thorn-headed and round-worms 

 the sexes are distinct, and may be often recognised externally 

 by their different form and size. In the thorn-headed worms the 

 sexual organs fill the greater part of the cavity of the body. From 

 the sheath that surrounds the proboscis there runs backward in the 

 axis of the body a band-like structure, which has been erroneously 

 supposed to be a canal, but which is for the support of the organs 

 that prepare the germ or the seed (ligamentum suspensorium) ; VON 

 SIEBOLD supposes that even the ovaries are developed in this organ. 

 These ovaries are found free in the abdominal cavity, as masses of 

 oblong-round eggs : the eggs become detached as they advance in 

 development. The muscular oviduct terminates in a very small 

 opening, scarcely visible at the posterior part of the body : it has at 

 its anterior extremity an infundibular expansion which alternately 

 widens and contracts, and takes up the eggs that were floating freely 

 in the cavity of the body and moves them onwards 2 to the oviduct. 

 This arrangement, in virtue of which the oviduct opens freely into 

 the cavity of the abdomen and is not an immediate continuation of 

 the ovary, is found in most vertebrates, with the exception of the 

 osseous Fishes, but has not hitherto been observed in invertebrates 

 except in EchinorJiynchus. In male thorn-headed worms there are 

 usually two testes lying one behind the other. The penis lies in a 

 sac having a conical appendage that can be everted from the body 

 in the form of a little bell. 



Amongst the Thread-worms the males are less frequent than the 

 females : they are smaller and more slender, and may frequently be 



1 See ESCHKICHT Anatomisck-physiologiscke Untersuckungen ueber die Bothrio- 

 cephalen; Act. Acad. Cces. Leop. Carol. Nat. Curios. Vol. xix. Supplem. n. 1840. 



2 VON SIEBOLD in BUKDACH'S Physiologic, n. s. 197. See a figure in BDROW 

 EchinorhyncJii strumosi Anatome. Diss. Zootom. Regiomonti, 1836, 8vo. fig. \g. fig. 6 ; 

 comp. DUJARDIN op. cit. p. 494, PI. vii. fig. 7, D 5. (Echinorhynchus anthuris, a species 

 from the freshwater Salamander). 



