PARORCHIS ACANTHUS, A NEW TREMATODE. 355 



poucli, and the symmefcrical-lobed testes. Looss does not 

 describe the form of the excretory system in the sub-family. 

 The genus is thus brought into close relation with a sub- 

 family, from which it differs externally, and affords a good 

 illustration of the point which Looss ^ insists upon, namely, 

 that external character is often a fallacious guide to the 

 systematic position of a form. 



EXPLANATION OF PLATE 21, 



Illustrating Mr. William Nicoll's paper on "Parorchis 

 acanthus, the Type of a new Genus of Trematodes.^^ 



The following letters apply to all the figures. Bs. Ventral sucker, D.St. 

 Yolk glands. Ex. Excretory system. /. Intestinal diverticula. K.St. 

 Ovary. K.O. Oviduct. L.C. Laurer's canal. M.S. Oral sucker. Oe. 

 (Esophagus. P. Penis. P.G. Geuital aperture. Ph. Pharynx. P. Ph. 

 Pre-pharynx. Pr. Prostate glands. T. Testis. Rs. Receptaculum seminis. 

 S.D. Shell gland. Tit. Uterus. Vg. Vagina. V.S. Vesicula seminalis. 



Fig. 1. — Parorchis acanthus, extended, slightly compressed. Ventral 

 aspect. Pa. Pre-acetabular ridge. Ex^. Lateral excretory trunk. 



Fig. 2. — Sagittal section through anterior part of body, a little to one side 

 of the middle line. Pa, Pre-acetabular ridge. 



Pig. 3. — Transverse section through genital aperture. 



Fig. 4. — Sagittal section throiigh ovary and shell gland ; almost median. 



Pig. 5. — Transverse section through receptaculum seminis and testes; 

 somewhat oblique. S.R. Collecting tubule. 



Pig. 6. — Miracidium larva, e.s. Pigment spot. 



1 ' Zool. Jahrb.,' Syst. xii, p. 596. 



VOL. 51, PART 2. NEW SERIES. 27 



