ell;obiopsidae 299 



partially dividing the left part of the organ of fixation from the larger right part. Now from this left 

 part the large roots take their origin (cf. also Fig. 7/?), and the whole configuration of this part of the 

 organ of fixation presents a striking similarity to that found in A.fagei (cf. Fig. gb). 



In A.fagei the organ of fixation has a rather thick cuticle (necessary to ensure a solid fixation of the 

 parasite in its host) ; part of this cuticle is pierced by a system of holes so that a sieve plate is formed 

 through which protoplasmatic excrescences (the roots) can protrude. In A.fagei the proximal parts of 

 these roots may also develop a cuticle, as in the specimen of Fig. gb. 



The external part of A.fagei does not show more than about fifty trophomeres, so that the parasite is 

 securely fixed to its host by means of the simple globular or oval organ of fixation. In A. umbellatiis, 

 however, which may have 750-1500 trophomeres, this enormous mass of external organs necessitates 

 the strengthening of the organ of fixation into an immovable organ of anchorage. Originally m the 

 specimen of A. iimbellatus described here the organ of fixation may have had a shape quite similar to 



Fig. 9a. Amallocystis umbellatus n.sp., type specimen. Section preceding the one of Fig. 8/;. Organ of fixation with sieve plate. 



/, organ of fixation ;/•, root, x 163. 

 Fig. 96. Amallocystis fagei Boschma, type specimen. Section of lower part of organ of fixation. /, organ of fixation ; p, proto- 

 plasmatic excrescences; s, sieve plate, x 283. 

 that found in A.fagei. It must have had a strong cuticle, but the part of the organ of fixation to the 

 left of the sieve plate in Fig. 9^ probably had a thin cuticle, so that the protoplasmatic excrescences 

 (the roots) might absorb food from the host. Gradually the root system became more divided and 

 more strongly developed ; at the same time the number of external parts (trophomeres and gonomeres) 

 increased, necessitating a stronger fixation of the parasite. The proximal parts of the root system 

 now became covered with a thick and strong cuticle, thereby forming a part of the organ of 

 fixation in securing a stronger hold of the parasite on its host. The sieve plate which was present 

 between the organ of fixation and the roots now had lost its direct function, but it remained as it was, 

 and the process of formation of a trabecular mass of cuticular excrescences even continued, so that now 

 in some parts two rows of trabeculae are visible. 



In the type specimen of A. umbellatus the sieve plate therefore appears to be an organ which has had 

 its use as long as the parasite was comparatively young and possessed a few trophomeres only. It has 

 lost its real function now, but it has remained where it originally developed. A comparison with the 

 sieve plate of A. fagei shows that the trabecular mass in A. umbellatus must be regarded as being 

 homologous with the former. 



The internal part of the organ of fixation forms a more or less bulbous expansion which is protracted 



