ON THE STRUCTURE OF PROTOPHRYA OVICOLA. 115 



females were found in which not a single normally developing ovum remained. The 

 membranes of the eggs were intact, but the eggs themselves were broken up into smaller 

 yellow spheres or irregular fragments some of which may have been ciliated. Dwarf, 

 abnormal, monstrous, or uncoiled embryos were sometimes seen in parasitized females. 

 I have often found this phenomenon of the breaking up of ova to be common among 

 many gasteropods in which a number of eggs are laid in one capsule, for instance 

 in Purpura, Urosalpinx, and Tergipes. In these cases, however, the unprotected 

 and disintegrating ova are utilized by the normal ones as food. In the case of the 

 disintegrating ova of Littorina rudis the fragments remain within their capsules and 

 they are not used, directly at least, as food by the normal embryos with which they 

 may be associated. The disintegration of the ova of Protophrya does not seem to 

 be an adaptive phase of nutrition, but a result rather of the presence of parasites. 



Protophrya does not itself devour the ova, nor does it mechanically modify 

 them in any visible manner. Its influence is probably a chemical one affecting the 

 growth of the ova adversely either directly, or indirectly by interference with the 

 glandular activity of the brood-sac. The products of the metabolism of the para- 

 sites may have a toxic effect upon the ova and the surrounding tissues comparable 

 with that which Vaullegeard (:01) has found in the case of the extracts of parasites 

 of vertebrates upon the tissues of their hosts. 



Superficially Protophrya bears some resemblance to Ancystrum mytili described 

 by Quennerstedt ('67) from the mantle cavity of the common mussel, but the absence 

 of oral aperture and pharynx at once make any relationship to this form remote. 

 A full examination of the literature indicates that both in its habitat and in its struc- 

 ture this parasite is somewhat unique. Schweier (:00) in his exhaustive discussion 

 of parasitic ciliates makes no mention of any form approaching this in structure or 

 host-relati onship . 



IV. STRUCTURE. 



The outline of the animal seen from the dorsal side is broadly elliptical with 

 symmetrical sides and somewhat similar ends (PI. VIII, Fig. 1). In some instances 

 the anterior end is slightly narrow and pointed, while the posterior one is broader 

 and more rounded, giving a slightly oval contour to the animal. The usual form, 

 however, is that shown in the figure. In lateral view (Fig. 2) the animal is seen to 

 be curved ventrally at the ends and sides, in fact around the whole edge, giving it the 

 form of a low helmet without visor or peak. In cross-section the animal is broadly 

 crescentic. The curved edges seen in lateral view cover an arc of 30 to 40 degrees 



