17] PROTEOCEPHALIDAE — LA RUE 17 



Proteocephalids was made until the work of the writer (La Rue, 1909) 

 on Ophiotaenia (Proteocephalus) filaroides. Subsequent work on the 

 histology of the cestodes of snakes has shown but little new, altho it 

 must be admitted that only little has been done on the group. 



The scolex is usually of small size and rather inconspicuous. Among 

 the fish Proteocephalids the heads range in size from a little more than 

 0.1 mm. in breadth to about 1. mm., tho in at least one species, P. sulca- 

 tus, the breadth of this region attains as much as 1.75 mm. Among the 

 amphibian and reptilian Proteocephalids the heads range from about 

 0.2 mm. to 1.75 mm. in breadth. In general the head is not sharply 

 delimited from the neck, which may be of nearly equal width or in 

 exceptional cases even wider for a short distance than the head. In 

 form the heads show considerable variation. They are usually more or 

 less globose or conical, and somewhat flattened dorsoventrally. In a 

 few cases the head may present a more or less flattened tetragonal 

 anterior face. The surface of the heads may be smooth or marked by 

 shallow or deep grooves between the suckers. As a rule the heads have 

 no folds or lappets of tissue about the suckers or on the anterior face. 

 Such structures are found, however, in Corallobothrium and to a more 

 limited extent in Choanoscolex. The special characters of the heads of 

 each species are taken up in the descriptive part of the work. The 

 heads of Proteocephalidae and Monticellidae differ from those of other 

 families of Tetraphyllidea in that the suckers are sessile, and have no 

 accessory areola. Even when the head is deeply furrowed the sucker 

 never has the appearance of having a stalk. Suckers may be prominent 

 or inconspicuous and so may influence the general appearance of the 

 head. 



A rostellum is unknown among the species of this family, altho 

 certain species have been erroneously reported to have such an organ. 

 It is possible, tho not probable, that some species of Acanthotaenia have 

 a rostellum. Some of these species have long apical prominences on the 

 head, but except for the elongation of this apex and the presence of 

 cuticular spines there is no evidence for considering this structure to be 

 a rostellum. The spines are not hooks but are cuticular structures which 

 may extend over the anterior part of the body. Neither elongated tip 

 nor cuticular spines are good criteria of the presence of a rostellum. 

 To determine the presence of a rostellum one should look to the inner 

 structure of the apex, its musculature and protrusibility, and to the 

 origin of this rostellum-like tip. In the tip of the heads of many species 

 which do not possess a functional fifth sucker there has been found a 

 peculiar structure consisting of massed cells and sometimes a few mus- 

 cular elements. This structure has been considered to be a rudimentary 



