HORMIDIUM. 



[ 395 ] 



HORN. 



the pseudo-thorax; cephalothorax articu- 

 lated to the abdomen, folding upon the 

 body. 



Two species ; on decaying fir-wood and 



roots. 



BIBL. Gervais, Walckenaer' s Apteres, m. ; 

 Claparede, Zeit. luiss. Zool. xviii. ; Murray, 

 Ec.Ent. 2-2-2-, Jti. Mic. Soc. 1880,177. 



HORMIDIUM. The group of species 

 of Ulothrix growing upon moist earth. 



HORMIS'CIA, Aresch. A genus of 

 Confervoid Algae, close to Ulothrix j with 

 the filaments jointed, usually simple, but 

 sometimes emitting ramules; cells with 

 thick, often lamellar walls ; propagation by 

 macro- and inicro-gonidia. Fresh and salt 

 water. (Rabenh. Fl. Alg. iii. 361.) 



HORMOS'PORA, Breb. A genus of Pal- 

 mellaceaa (Confervoid Algae), with a frond 



Fig. 336. 



Fig. 337. 



Hormospora transversalis. 

 Fragments of gelatinous filaments, with the cells 



grouped in fours. 

 Magnified 350 diameters. 



consisting of simple or branched gelatinous 

 confervoid cords enclosing rows of oval or 

 spherical cells ; they are found floating 

 among Confervas or other aquatic plants, 

 and appear to the naked eye like greenish 

 filaments. These plants do not appear to 

 consist of septate filamentous tubes like the 

 Confervse, but of rows of individual cells 

 imbedded in a filiform gelatinous tube 

 (fig. 336), analogous in its nature to the 

 gelatinous coat investing the linear rows ol 

 cells of Hyalotheca, &c. The cells multiply 

 by transverse division, the rows thus becom- 

 ing elongated; these cells contain green 

 contents arranged in a granular, lamellar, 

 or radiating form. Brebisson describes ob- 

 scurely another mode of increase, in which 

 the " endochrome becomes concentrated anc 

 organized into vesicles or zoospores. Th 

 corpuscles then become larger ; and the fila- 

 ment becoming as it were dislocated, the 

 corpuscles group themselves in several rows 

 and without regular form " (fig. 337). In 



H. transversalis there is an especial tendency 

 to a grouping of the cells in fours. Five 

 species have been described j 1 and 3 are 

 known as British. 



H. mutabilis, Breb. Filaments simple ; 

 cells ovoid or subspherical j cell-contents 

 lamellar ; freshwater. Breb. Ann. Sc. Nat. 

 3 ser. i. pi. 1. fig. 1. 



H. transversalis, Breb. (figs. 336, 337). 

 Filaments simple ; cells ovoid or fusiform, 

 transverse ; contents granular j freshwater. 

 Breb. I. c. fig. 2. 



H. ramosa, Thwaites. Filaments 

 branched ; cells oval or spherical j contents 

 radiated. In a pool to which salt water 

 had access. Harvey, Phyc. Brit. pi. 213. 



BIBL. Brebisson, Ann. Sc. Nat. 3 ser. i.; 

 Harvey, Br. Mar. Alg. 235, pi. 27 B, Phyc. 

 Brit. pi. 213 ; Nageli, Einzell. Alg. 7, pi. 3. 

 fig. B ; Rabenhorst, Fl. Alg. iii. 48. 



HORN. The horns of animals are of 

 three kinds, those composed of bone, those 

 consisting of epidermic formations, and 

 those in w T hich both are present. The former, 

 properly called antlers, agree in minute 

 structure with bone, and therefore require 

 no special notice. The horn of the rhino- 

 ceros may be taken to represent the structure 

 of the second kind. It consists of an aggre- 

 gation of horny fibres, each of which is made 

 up of a series of concentric layers. These 

 layers are composed of cells tangentially flat- 

 tened, and sometimes containing pigment. 

 The cells may be separated by macerating 

 the horn in solution of potash. Cracks 

 filled with air are frequently visible between 

 the layers. The centres around which the 

 laminae are arranged probably correspond to 

 papillae of the cutis. The horn of the 

 buffalo agrees essentially in structure with 

 that of the rhinoceros. 



The third kind of horn is exemplified by 

 that of the cow. In its centre is a process 

 of bone, surrounding and extending beyond 

 which is the proper horn, consisting of con- 

 centric layers, in the natural state composed 

 of flattened, irregular, angular, nucleated 

 cells (PI. 22. fig. 29 ), which assume their 

 primitive forms under the action of potash 

 (6) ; some of them contain pigment (d). 

 Between the laminae, cracks containing air 

 are also met with (f). 



Sections of horn made at various angles to 

 the axis, form very beautiful polarizing ob- 

 jects ; the gorgeous colours seen in those of 

 rhinoceros's horn cannot be excelled, nor can 

 drawings represent them faithfully (PL 39. 

 figs. 37, 38). The horn of the buffalo 



