AVIAN CESTODES. 591 



of hooks present on the rostelkim ; v. Linstow gives the number 

 found by himself as 180. I find in my species something 

 between 120 and 130. These hooks are, as in other Darainea, of 

 the well-known hammer-shape so characteristic of the family 

 Davaineidfe. 



The hooks really form two concentric rows, wliich arrange- 

 ment is only clear in sections which pass through the " ha.ndle " 

 part of the hook ; that they are of different sizes is only shown 

 in the " head"' of tlie hammer, where one series is much shorter 

 than the other ; I could find no such difference in thickness in 

 the " handle '' region of the hooks. An alternation between 

 lai'ger and smaller hooks is stated by Parona to occur in his 

 species. The hooks are of course implanted upon the edge of the 

 circular rostellum. They are of the usual golden-brown colour. 

 Von Linstow has represented the hooks of his examples, called 

 by him TiTvia strnthionis, as being weak and frayed out at the 

 point of implantation. I have found nothing of the kind in the 

 robust (though small) hooks of the examples examine.d by 

 myself. 



My own observations a,re in fact more in accord with those of a 

 later investigator than those referred to. Dr. ZillufF*, referring 

 only to V, Linstow's paper and not to that of Parona, naturally 

 finds differences to record (" naturally " if I am correct in 

 thinking that v. Linstow's specimens are of another species than 

 that which Parona and I describe). He emphasizes the i-ostellum 

 and gives the diameter of the scolex as I'S'S ram., the dimensions 

 agreeing with mine rather than with Parona's. But this author 

 does not mention from what species of Siruthio he obtained the 

 material. 



The sucker's are not armed, as is the case in certain other 

 members of the genus, a great pa.rt of the species of which have 

 armed suckers. I believe that I can state this fact positively. 

 Excepting where the retractor muscles are attached to the 

 suckers, the latter lie for the most part free within the cavity of 

 the scolex to which they are fitted. A space is generally visible 

 between sucker and body-wall. Although there is no apparent 

 difference that T could detect between the individual suckers, I 

 have noted in this worm a means of distinguishing the dorsal 

 from the ventral couple. The two dorsal vessels, instead of 

 ending in the medullary region like the ventral vessels of the 

 water-vascular system, bend dorsally, each of them perforating 

 the layer of longitudinal muscles of the cortex ends in the 

 neighbourhood of one of the suckers. The exact mode of ending 

 I did not ascertain. It is. therefore possible to distinguish two 

 of the suckers as belonging to the dorsal surface. The characters 

 of the musculature of the scolex I shall deal with later in 



* " Vergleichende Studien iibei" die Muskulatur des Skolex der Cestodrn." 

 Iiian<r.-Diss. Univ. Zurich, 1912. (Publisbod also in Anh. f. Xatm-o-. of the sanie 

 j-ear.) See also Liilie in Zool. Auz. xvii. 1891, p. 2sO. 



41* 



