and other Indigenous Rhizopods. 439 



my arrangement, comprises the Gromida, Foraminifera, and 

 Polycystina. In these families, the nuclear granules are diffused, 

 and assume the multiple character of sarcoblasts, which, on 

 separation from the parent sarcode, constitute the rudiment or 

 "primordial segment" of the new brood. 



In my experience, the contractile vesicle does not make its 

 appearance either in the Herpnemata (which constitute the first 

 or lowest order) or the Protodermata or second order (which 

 comprises the Thalassicollidae, Acanthometrina, and their allies), 

 but occurs, for the first time, in the third order or Proteina, in 

 which I associate the Actinophryna, Lagynidce, and Amcebina — 

 the name of this order being adopted from the classification of 

 MM. Claparede and Lachmann, who, in like manner, associate 

 Actinophrys and Amoeba, but on widely different grounds from 

 those that have led me to assume their ordinal unity. 



In the third order both nucleus and contractile vesicle, I be- 

 lieve, are invariably present, although naturally difficult of detec- 

 tion in the testaceous genera. The latter organ, however, in so 

 far as my experience of living representatives of nearly every 

 important form enables me to arrive at a correct opinion on the 

 subject, ought not to be regarded as a definite-walled contractile 

 sac, distinct in composition from the remainder of the proto- 

 plasmic matter, but simply as a specialized vacuolar cavity formed 

 out of a portion of the ectosarc. 



Mr. Carter, in his paper on the Organization of the Infusoria, 

 already referred to (I. c. p. 130), says, " That the vesicula is a 

 distinct organ, and not merely a space like the digestive globule, 

 might be inferred from its always appearing in the same place 

 in the same species"*. For reasons already adduced, I am in- 

 clined to regard it in an opposite light — that is to say, as merely 

 a space bounded by a layer of ectosarc, and not by a membranous 

 wall of distinct origin and character. And I think my view will 

 be at once recognized as correct when it is taken into considera- 

 tion that we constantly see multiple contractile vesicles, not only 

 already formed, but actually forming under our eyes and again 



* On reference to what has been stated in a preceding page, it will be 

 seen that Dr. Carpenter speaks of the nuclear capsule as " a clear flattened 

 vesicle ; " whilst he considers the contractile vesicle to be " a vacuole with 

 a defined wall " (Introduction to the Study of the Foraminifera, p. 14). 

 Mr. Carter, again, describes the nucleus as discoid in shape, and fixed to 

 one side of a transparent capsule, whereas he refers to the contractile organ 

 as " distinct and not merely a space like a digestive globule." In directing 

 attention to these definitions, I am desirous of showing that both these 

 authorities express their opinions on the subject with a degree of reserve 

 which was fully warranted under the circumstances, but which leaves the 

 proofs as to the existence of a true membranous vesicle in one case depend- 

 ent on equal proofs of its existence being forthcoming in the other. 



