HOLOSTICIIA. 



[ 394 ] 



HOPLOPHOEA. 



rounded or truncate in front ; no lips nor 

 teeth ; cilia arranged in longitudinal rows. 



Ehrenberg admits six freshwater species ; 

 to these Dujardin, who places this genus in 

 the family Paramecia, adds one marine. 



H. ovum, E. (PI. 31. fig. 22). Body ovate, 

 subcylindrical, ends subtruncate ; internal 

 substance green : length 1-570 to 1-210". 



H. hrunnea, D. (PI. 31. fig. 21). Body 

 brown ; cylindrical, becoming globular when 

 distended with food, and then changing in 

 colour; length 1-120". 



The eucysting-process has been observed 

 in two of the species. 



BiBL. Ehrenberg, Inf. 314 ; Dujardin, 

 Inf. 493 ; Cohn, Bieh. und Koll. Zeitschr. 

 iv. ; Stein, Inf. ; Kent, Inf. 498. 



HOLOS'TICHA.— A genus of Hypo- 

 trichous Infusoria (Kent, Inf.). 



IIOLOTHURID'EA (Sea-slugs).— A fa- 

 mily of Echiuodermata, of the order Pedi- 

 cellata. 



Interesting to the niicroscopist, from the 

 presence of curious calcareous plates, &c. 

 existing in the integument. 



See ECHINODKRMATA. 



HOLO'THYRUS, Gerv.— A genus of 

 Gamasea (Acariua). 



II. coccinella is nearly as large as a lady- 

 bird (Coccinella), and is found in the Isle of 

 Erance. 



Blbl. Gervais, Walckenaer'' s Apth-es, iii. 



IIOMALOCOC'CUS, Kutz.— A genus of 

 Coufervoid Algpe, consisting of cells united 

 into flat oblong irregular corpuscles, en- 

 closed in a spherical gelatinous sheath. 



H. Ilassallii ; green, size of a pea or nut ; 

 in stagnant pools. (Eabeuli. Fl. Alg. 09.) 



IlOMffiOCLA'DIA, Ag.— A genus of 

 Diatomacese. 



Char. Frustules those of Nitzschia, ar- 

 ranged in tufts within gelatinous tubes, 

 which form a filiform, usually branched 

 frond. Marine. 



H. Martiana, Ktz. {II. am/lica, Ralfs) 

 (PI. 19. fig. lo : (t, portion of frond ; h, part 

 of a filament containing two frustules; c, 

 front view of single frustules, with endo- 

 clu'ome ; d, side view of empty frustules). 

 Frond simple or dichotomously divided, 

 rugose ; entire plant 1 to 2" high. 



Il.fiUfonnis. Erond linear, simple, tufts 

 containing three or four frustules. 



Il.sifinioidea. Frond linear, simple ; frus- 

 tules sigmoid. 



Rabenhorst describes 8 European species. 



BiBL. Kiitzing, Bacillar. 110, and Sp. Ah/. 

 97; Ralfs, Ann. ^\ II. 1845, xvi. 109; 



Smith, Br. Diat. ii. 80; Eabenhorst, Fl. 

 Alff. i. 160. 



HOM'OPUS, Furst.— A genus of Hypo- 

 pidte (Acarina). H. elephantis, found on 

 the dried skin of an elephant, = the hypopial 

 nymph of Acarus dumesticus, Megnin. 

 (Fiirstenberg, Kriitzmilhen, 222 ; Miu-rav, 

 Ec. Ent. 253 (fig.) ; Megnin, Paras, l-il .) 



HOOF. — The hoofs of animals consist of 

 the same structure as horn. 



HOOKE'RIA, Smith.— A genus of Hyp- 

 noid Mosses. 



Two species, on moist banks and wet 

 rocks. 



BiBL. Wilson, Bryol. Brit. p. 415. 



HOP. — Thehop plant {Humuhis Liipidus) 

 is remarkable for the glands containing the 

 resinous secretion imparting the aromatic 

 odour. These occur on the lower face of 

 the leaf, upon the calyx, and above all, on 

 the scales of the fruit and the seed-coat. 

 They have been examined by Meyen and 

 others, mostly recently by Personne. They 

 are little stalked cups (PI. 2S. fig. 14) com- 

 posed of a single layer of cellidar tissue, 

 concave above at first ; but as the secretion 

 increases in quantity, the cuticle becomes 

 detached in a plate from the upper surface, 

 except at the rim of the cup, and is pushed 

 up so as finally to form a convex papilla on 

 the top, like the nut projecting from an 

 acorn-cup. The secretion appears to be 

 formed in the cells, and poured out beneath 

 the cuticular pellicle, which is marked with 

 lines corresponding to the side-walls of the 

 cells. Solution of potash and alcohol clean 

 awaj" the resinous secretion, and render the 

 structure clear. When the fresh glands are 

 placed in water, they swell, and finally burst, 

 the cuticidar lid usually separating by a cir- 

 cumscissile dehiscence. 



The hop is subject to a peculiar mildew, 

 a minute fungus, for which see Ekysiphe 

 {Sphcerotheca). 



BiBL. Meyen, Secretions- Organe d. PJlan- 

 zen, 38, pi. 5. figs. 17-21 ; Personne, Ann, 

 Sc. N. 4 ser. i. 299, pi. 17. 



HOPLITOPIl'RYA, St.— A genus of 

 Ilolotrichous Infusoria. 



Char. Ovate or elongate, mouthless, with 

 a ventral anterior band or one or more 

 hooks. Internal parasites. Seven species : 

 in tlie intestine of Lumbrici, Plunarice, &c. 

 (Kent, /?(/: 571.) 



HOPLC)ri]'ORA, Koch.— A genus of 

 Oribatoa (Acarina). 



Char. Body and general habit those of 

 G alumna, but no wing-like appendages to 



