ACHROMATISM. 



ACINETINA. 



ACHRO'MATISM. A term properly 

 signifying freedom from chromatic aber- 

 ration, but commonly used to denote free- 

 dom from both spherical and chromatic 

 aberration. 



A GIG UL A'RIA, D' Archiac. One of the 

 Foraminifera imperforata, related to Dac- 

 tylopora, and consisting of numerous cham- 

 bers arranged in close order side by side 

 without intercommunication, and forming 

 minute aciculate cylinders, or narrow ta- 

 pering plates. Known fossil only in some 

 Tertiary beds of France. 



BIBL. Carpenter, Introd. Foram. 137. 

 ACINE'RIA, Duj A genus of Infusoria, 

 of the family Trichodinia. 



Char. Body oblong or lanceolate, de- 

 pressed, the fore part somewhat obliquely 

 recurved like the blade of a sabre ; a row of 

 cilia,directed forwards, arising from one side. 

 Differs from Trachelius, Duj., in the ar- 

 rangement of the cilia and in the anterior 

 curvature ; devoid of a mouth, like Trache- 

 lius, which especially distinguishes the pre- 

 sent genus from Pelecida. 2 species : 



A. incur vata (PL 30. fig. 1) ; marine, 

 colourless; length 1-590 inch. 



A. acuta (PI. 30. fig. 2), found in fresh 

 water ; length 1-580 inch. 



Dujardin figures in the latter species cilia 

 upon both margins, those on one side being 

 directed forwards, and those on the other 

 backwards. 



Claparede and Lachmann refer these to 

 AmpMleptus. 



BIBL. Dujardin, In/us, p. 402 ; Clap, and 

 Lachm. Inf. p. 356. 



ACINETA, Ehr. A genus of Rhizo- 

 poda, belonging to the family Acinetina. 



Claparede and Lachmann enumerate 8 

 species. 



A. mystacina (PL 51. fig. 11). Yellowish 

 brown, rounded, tentacles in two bundles j 

 1-120 to 1-800. On Lemna minor. 



A. patula (PL 51. fig. 12). Body as if 

 resting on a cup-shaped carapace, variable 

 in form; contains brown granules. On 

 marine Algse. Norway. Length 1-100". 



A. tuberosa (PL 30. fig. 4). Colourless 

 or yellowish brown, triangular when ex- 

 panded; tentacles arising from the distal 

 angles only. Salt or brackish waters; 1-1CO" 

 to 1-410". 



A. Lynybyi, ferrum-equinum, and cylin- 

 drica are "referred by Ci. and Lachm. to 

 Podophrya. 



A. Notonectce. On the hairs of the legs of 

 N. f/lauca. 



BIBL. Pineau, Ann. d. So. Nat. 3 s6r. Zool. 

 iii. & ix.; Ehr. Inf.; Duj. Inf.; Claparede 

 and Lachmann, Etudes, '$c. ;' Ann. N. H. 

 1857, xix. ; Stein, Infus.; Gegenbaur, 

 MorpJi. Jahrb. 1875. 



ACINETI'NA,Ehr. A family of Radio- 

 larian Rhizopoda. 



Char. Those of the Actinophryina, but 

 with usually capitate and suctorial tubular 

 tentacles, the body being more or less en- 

 closed in a carapace, which is generally 

 prolonged to form a stalk. 



The structure and relations of these ani- 

 mals are still very unsettled. The re- 

 searches of Pineau and Stein tended to 

 render the existence of the species doubtful, 

 by showing that they were stages of deve- 

 lopment of Epistylis, Vaginicola, Vorticetta, 

 &c. ; but this has since been found to be in- 

 correct. They exhibit a nucleus, and one 

 or more contractile vesicles. The remark- 

 able suctorial character of the tentacles has 

 not been proved to occur in all the genera 

 and species. Many, however, have been 

 seen to take food voraciously, which is thus 

 effected : when an Infusorium touches the 

 button-like end of the tentacle, it usually 

 remains adherent to it ; the end becomes still 

 more dilated so as to constitute a sucking 

 disk, and the ray becomes thicker and 

 shorter, the other rays at the same time 

 making grasping moVements and endea- 

 vouring to attach their extremities to the 

 captured prey. A current of chyme-par- 

 ticles is then soon seen running 'from the 

 captured infusorium into the body of the 

 Acineta. The chyme-particles form at first 

 a slender row,but afterwards collect in a drop. 

 The body of the Acineta then becomes 

 opaque, from the collection of the drops. 



The colourless or coloured ova described 

 by Ehrenberg are partly chyme-particles, 

 partly oil drop-like globules which make 

 their appearance in the AcinetcB after ani- 

 mal food. The ciliated swarm-germs to 

 which they give origin have been traced 

 directly into Acinetce. Fission has been 

 observed in Acineta mystacina, not in the 

 others. The genera may be thus divided : 



^Tentacles not borne upon a proboscis. 

 Tentacles unbranched. 

 . Stalks simple. 



(A peduncle 1. Podophrt/a. 



No shelH No pedun- (free .. 2. Spkarophrya. 

 I cle } fixed. 3. Trichophrya.] 



A a \,^-i j Peduncle present . 4. Acineta. 



1 1 Peduncle absent... 5. SolenopJirya. 



Ftalks branched 6. Dendrosoma. 



Tentacles branched 1. Dendromycetes. 



**Tentaoles borne on a long pro- 

 boscis 8. Ophryodetidrion. 



