ON TURBELLARIA OF THE SCOTTISH NATIONAL ANTARCTIC EXPEDITION. 821 



The aperture lies just in front of the sucker ; the shell-gland portion is short and 

 dilated and has highly glandular walls. The tissue surrounding it, as well as that around 

 the lower end of the uterine duct, is crammed with granules. The uterine duct, which 

 is dilated, but empty in both specimens, is lined by cells possessing remarkably long 

 cilia, and passes backwards below the gut, to end in the two uteri into which the 

 oviducts open. The ovaries are found throughout the lateral parts of the body, dorsal 

 to the testes. Many of the ovarian tubes contain yolk-like material, which seems to 

 be derived from the transformation of cellular elements within their walls. This 

 arrangement seems to replace the special uterine glands described as occurring in 

 Aceros inconspicuus and certain other Euryleptidce. 



Systematic. 



The specimens described above may be included in the Euryleptid genus Aceros, 

 Lang, as amended by Plehn (2). The original description of the genus is as follows (1) : 

 — Korper glatt ; Mund unmittelbar hinter dem Gehirn ; Pharynx cylindrisch ; Haupt- 

 darm mit circa fiinf Paar Darm-ast-wurtzeln ; Darm-aste nicht anastomosirend ; mann- 

 liche Oeffnung sehr nahe hinter dem Mund ; mannlicher Begattungs-apparat unter dem 

 Pharyngeal-tasche ; weiblicher mit seiner Oeffnung dicht hinter derselben ; ein Paar 

 Uterus-drusen ; sehr wenige Augen (jederseits drei) im Gehirn-hof; sehr wenige Augen 

 in je einer seitlichen Gruppe am vorderen Korper-rande an der Stelle wo bei den 

 verwandten Gattungen die Tentakeln stehen die bei dieser Gattung fehlen. 



Two species of Aceros have been described, viz., A. inconspicuus, Lang (1), the 

 species for the reception of which the genus was founded, and A. nationalis, Plehn (2). 



A. inconspicuus, from the Gulf of Naples, is a small member of the genus measuring 

 3 mm. long by 1"3 mm. broad. The dorsal surface is mottled, owing to the presence of 

 finely granular pigment under the basement membrane. Over the brain there are two 

 groups of three eyes, the outermost eye on each side being deeply sunk and lying on 

 the outer anterior surface of the brain. There are four marginal eyes on either side, 

 evidently in the position of the absent marginal tentacles. The mouth is in front of 

 the end of the first body fourth. The male opening is close behind the mouth ; the 

 female opening is a little in front of, and the sucker a little behind, the middle of the 

 body. 



A. nationalis, from the neighbourhood of Cape St Vincent, is larger, measuring 

 5 mm. by 2 -5 mm., and has a large cylindrical pharnyx, which in the retracted condition 

 measures one-fourth of the body length. The mouth is at the beginning of the second 

 body sixth, the male opening at the end of the second body fifth, and the female 

 opening almost exactly in the middle of the body. Behind this lies the sucker, which 

 is large and muscular. Over the brain area there are two groups of eyespots each 

 containing twelve to fifteen ocelli. The marginal ocelli are about thirty on either side. 



For the reception of A. nationalis within the genus Aceros, Plehn amends Lang's 



