or THE VORTICELLLNA. 



595 



it, a current of water, together with the nutritive particles it may contain. 

 Within are a curved semicircular band-like nucleus, a contractile vesicle, the 

 so-called stomach-sacs or vacuoles, and numerous granules and molecules. 

 The mouth opens into a wide oesophagus, which extends backwards towards 

 the centre of the body, where it terminates abruptly. The stem essentially 

 differs from that of Carchesium in its central canal being continuous through- 

 out ; but the distinction drawn between the two genera by Ehrenberg, from 

 the presence of dissimilar corpuscles (animalcules) being found in Zootham- 

 niuni, and not in CarcJiesium, is worthless, as that cii^cumstance is indicative 

 of nothing more than a certain condition of development. The oldest portion 

 of the stem in this genus often becomes soKd and rigid, and thereby re- 

 sembles that of Epistijlis, for which it might he mistaken (see p. 293). Dr. 

 Wright observes that the primary (parent) zooid of a polypary does not begin 

 to develope the contractile band in its pedicle until this has attained a con- 

 siderable length ; hence, for the time, this primary zooid is an Epistylis by 

 the structui-e of its stalk. 



ZooTHAMNitTM Arbuscula (Vorticella 

 racemosa, M. and Duj.) (xn. 67, 68, 69) 

 has the branches in racemes or irre- 

 gular umbels ; coi^puscles (zooids) white, 

 campamdate ; pedicle very thick. These 

 beautiful little trees resemble plumes of 

 feathers. They have the characters of 

 Carchesium aud Opercularia as respects 

 the presence of globular bodies in the 

 axillee of the branches, but are at once 

 distinguished by the strength of the 

 latter. Found upon Ceratophyllum and 

 other freshwater plants, and also in sea- 

 water ; \-isible to the naked eye. It con- 

 tracts itself on its very elastic pedicle on 

 every alarm. It lives but a short tune 

 when removed from its native place 

 (BrightweU, p. 344). Size 1-430" ; tree 

 1-4", stalk one-fom*th the thickness of 

 the body. 



Z. nivmni (Z. plumosum, Wright). — 

 Main stem zigzag ; branches short, alter- 

 nate, almost yerticUlate, given off from 

 each angle of stem ; zooids oblong, cam- 

 pamdate, white, clustered at the ends of 

 the branches, which are filiform, the 

 lower ones often deserted, while the 

 upper bear clusters of club-shaped little 

 bodies rounded anteriorly. Summit of 

 main stem and branches curved back- 

 wards like an ostrich-feather ; hence the 

 name plumosum, proposed by Dr. Wright. 



Z. affine (Stein). — Stem dichotomous ; 

 branches attaining a nearly equal eleva- 

 tion. The primary stem varies in length 

 as well as the lateral ramifications ; hence 

 the arborescent polypidom varies con- 

 siderably in its general aspect, being at 

 one time loose and diffiise, at others com- 

 pact and dense. When extended, the 



transparent branches are smooth, but 

 dming contraction are thrown into trans- 

 verse folds, and acquire a relative in- 

 crease of thickness. The canal is con- 

 tinuous throughout, except at the base of 

 attachment in specimens of some age, 

 where the stem is solid -, in its interior 

 is the axis-matter, — i. e., in Ehrenberg's 

 language, the muscle moving the stem. 

 The animalcides borne on the extremi- 

 ties of the branches are oval, somewhat 

 contracted behind, and truncate in front, 

 where they are surmoimted by a thick 

 tumid peristom of rather less diameter 

 than that of the body. The rotary organ 

 is strikingly narrower, and protrudes 

 little beyond the peristom : in the course 

 both of the extension and retraction of 

 the rotary disc a fold is produced, which 

 gives the appearance of a double peri- 

 stom. A wide oesophagus and digestive 

 tube opens from the mouth ; and near its 

 posterior extremity is the contractile 

 vesicle. The nucleus resembles a short 

 semicircidar band, and lies across the 

 body. The relative thickness of the stem 

 is a remarkable character of this species, 

 being one-half that of the animalcules it 

 supports. Usual length of animals 1-380" 

 to 1-270' , 

 Entomostraca, &c. 



Z. Parasita (Stein). — Tree-like poly- 

 pary, very small, supporting few animal- 

 cules : the latter agree in figure with 

 those of Z. Arbuscula. Stein believes it 

 identical with Carchesium pijgm<mim, 

 Ehr,, the latter being an incompletely- 

 developed form. On Entomostraca and 

 small aquatic Crustacea. 



We are indebted to Dr. Wright for a 

 notice of the following species : — 



2q2 



