and other Indigenous Rhizopods. 437 



parent capsule, which, being more or less larger than the nucleus 

 itself, causes the latter to appear as if surrounded by a narrow 

 pellucid ring"*. 



Now, whilst both these observers speak to a vesicular boun- 

 dary to the nucleus, it is evident, I think, that they do not 

 allude to that highly specialized membranous covering which 

 is so remarkably manifest in A. villosa, and is actually sepa- 

 rable from the body. The point is not so immaterial as it 

 would seem to be at the first glance, inasmuch as a definite 

 vesicular covering has also been supposed by Claparede and 

 others to appertain to the contractile vesicle of Actinophrys, 

 whereas, as I shall presently endeavour to show, none is in 

 reality present either in the contractile vesicle of that genus or 

 of Amoeba ; and hence the character becomes to this extent a 

 distinctive one. Moreover it is important from its at once 

 stamping as complete the analogy I desire to draw between the 

 nucleus of Amoeba and of Plagiocantha, Thalassicolla, Acantho- 

 metra, and Dictyocha, whereby the relation of the several parts 

 to each other in these genera although belonging to a distinct 

 order, becomes intelligible. 



The position of the nucleus in Amoeba villosa has already been 

 shown to be variable. I am not aware that, under any circum- 

 stances, the nucleus of this form can strictly be said to adhere 

 to the inner portion of the ectosarc, as indicated by Carpenter, 

 or to be situated on the outer portion of the endosarc, as stated 

 by Carter — its temporary location in the vicinity of the villous 

 patch, spoken of in my former paper, being due, as I conceive, to 

 that more highly differentiated condition of the posterior part of 

 the organism which constitutes so striking a feature in A. villosa. 

 I have as yet been unable to ascertain positively the manner in 

 which both nucleus and contractile vesicle are periodically sus- 

 tained near the villous patch ; but, from the constricted shape 

 frequently assumed in this region, and the tendency to project 

 the pseudopodia principally from the advanced or anterior por- 

 tions of the body, there can be little doubt that it is brought 

 about by the augmented contractile power of the posterior ex- 

 tremity. On the same hypothesis we may account for that 

 peculiar state in which a mass of granular matter, resembling 



* On the Organization of the Infusoria, Ann. Nat. Hist. ser. 2. vol. xviii. 

 p. 221. 



Mr. Carter is of opinion that there is a central cavity in Amoeba, at times 

 distensible with water. Thus he speaks of an " Amoebous cell under 

 spherical distension." This may account for the view held by him with 

 regard to the position of the nucleus in the Bombay form; but I must 

 distinctly observe that no such cavity is present in A. villosa. (Ann. Nat. 

 Hist. vol. xviii. p. 223, and explanation appended to fig. 1. plate 5, accom- 

 panying his paper.) 



