THE CESTOIDEA 



communication with the exterior by a " birth-pore." In the second 

 type, this pore has been lost, so that the uterus is a closed sac 

 (Fig. XIII. ). In the former case, the eggs when ripe can pass out 

 from time to time without a necessary separation of the proglottids ; 

 whereas, in the second case, the ripe proglottids drop off from the 

 strobila, either singly or in groups, and the eggs are discharged 

 only by local dehiscence or decay of its walls. 



Associated with the possession of a birth-pore is the existence 

 of only two adhesive organs of the scolex, whereas those Cestodes 

 without a birth -pore possess four such organs, except in a few 

 individual instances, where there is then evidence of fusion. These 

 characters serve to differentiate the grade Merozoa into two 

 branches the Dibothridiata and the Tetrabothridiata. 



These " organs of the scolex," comprehensively grouped as 

 " suckers," occur in the Merozoa under three well-marked forms : 



FIG. XIII. Diagrammatic longi- 

 tudinal median sections (or 

 rather projections) of a pro- 

 glottid. 



1. Dibothridiata. 2. Tetraboth- 

 ridiata, showing the uterine pore 

 in the former; its absence in- the 

 latter, a, common genital (copu- 

 latory) pore ; b, cirrus ; c, vas de- 

 ferens and testes ; d, vitellaria ; e, 

 vitello - duct ; /, gerinariuin ; g, 

 ootype, surrounded by shell glands ; 

 h, vagina (with dilatation or sper- 

 matheca) opening into the genital 

 atrium ; i, the uterus, opening ex- 

 ternally at j, in the Dibothridiata, 

 but a blind sac in the Tetraboth- 

 ridiata. 



A ff 



(a) as sucking grooves or "bothria," which are narrow fissures or 

 widely open cuppings on the dorsal and ventral surfaces of the 

 head; their muscles are only slightly developed, and are not de- 

 limited internally from the parenchyma; they are characteristic 

 of the Dibothridiata ; (b) as " phyllidia " (or " bothridia," M. 

 Braun 1 ), which are essentially outgrowths from the side of the 

 scolex, to the number of four. Each is more or less distinctly 

 concave distally ; this muscular cup is the " bothridium," the 

 margins of which, and indeed the entire structures, are extremely 

 mobile ; and Pintner has suggested that these are rather organs of 

 locomotion than of attachment. They present certain modifications 

 (see below), and are characteristic of the Tetraphyllidea, Diphyllidea, 

 and Tetrarhyncha. Finally, (c) as "acetabula," or suckers in the 



1 Van Beneden used the term "bothridium " for all kinds of sucking organs in the 

 Cestoidea. Earlier writers used "bothrium." Braun uses "bothridia" for those 

 which are here termed " phyllidia," and I restrict the use of the term to the cup or 

 sucker carried by the phyllidimn. 



