POMPHOLYX. 



[ 528 ] 



PORPHYRA. 



but the ciliated spermatozoids (PI. 32. fig. 

 33) escape and swim actively in the water. 

 They require at least an eighth object-glass 

 for examination, and the cilia are seen most 

 clearly after drying the object, or treating with 

 tincture of iodine. 



BIBL. Wilson, Bryol. Britann. p. 205 et 

 seq. ; Thuret, Ann. des Sc. nat. 3 ser. xvi. 

 p. 26. pi. 14. 



POMPHOLYX, Gosse. A genus of Ro- 

 tatoria, of the family Brachionaea. 



BIBL. Gosse, Ann. Nat. Hist. 1851. viii. 

 p. 203. 



PONTIA, Fabr. A genus of Lepidopte- 

 rous Insects, of the family Papilionidae. 



This genus contains some of the com- 

 monest butterflies, as P. brassica, the large 

 cabbage-butterfly ; P. rapes, the small cab- 

 bage-butterfly; and P.napi, the green- veined 

 white butterfly. 



The form and structure of certain scales 

 existing upon the under side of the wings of 

 the males are curious; and the markings 

 were formerly found so difficult to render 

 distinct, that the scales were used as test- 

 objects. 



In the male P. brassicce the upper surface of 

 the anterior wings is free from spots, whilst in 

 the female there are two black spots in that 

 situation. The peculiar scales are repre- 

 sented in PI. 27. fig. 24 ; fig. 26 exhibits a 

 portion of the wing with the ordinary scales. 



In P. rapce and P. napi the anterior wings 

 of the males have a single spot upon the 

 upper surface, whilst there are two upon 

 each wing in the females. The peculiar 

 scales bear considerable resemblance in the 

 two species (PI. 27. fig. 23 a, scale of P. rapa; 

 fig. 23 b, portion of wing, snowing the points 

 of attachment of the two kinds of scales). 



The scales may be separated by gently 

 pressing the under surface of the wings 

 against a slide. 



See SCALES OF INSECTS and TEST- 

 OBJECTS. 



BIBL. Westwood, Brit. Butterflies. 



POPPY. The seeds of Poppies (Papaver, 

 L., Nat. Order Papaveraceae) are elegant 

 opaque objects under a low power, the testa 

 being pitted so as to produce a reticulated 

 surface (PI. 31. fig. 14). 



POROSITY OF BODIES. That all bo- 

 dies are porous to a greater or less degree, 

 allowing vapours and gases to pass through 

 their substance, is an established fact in 

 physics and physiology. The passage of 

 solid particles, also, as charcoal and sul- 

 phur, through certain organic tissues in which 



no apertures have hitherto been detected, as 

 the ^kin and mucous membranes, has re- 

 cently been attested by several observers. 



M. Keber believes that he has detected 

 the existence of pores in all bodies of what- 

 ever kind ; these he finds in the dots, streaks 

 and irregular markings, from 1-11,000 to 

 1-45,000" in diameter, visible in minute and 

 thin scrapings and fragments of solids, as 

 particles of dust, scrapings from a piece of 

 bladder, &c. This view does not require a 

 serious refutation. Of evidence that the 

 markings are pores, there is none ; and on 

 examining a thoroughly cleaned and thin 

 piece of the membrane of a vegetable cell, we 

 do not perceive anything corresponding to 

 pores. If the true pores are ever detected 

 by the microscope, there can be little ques- 

 tion that they will exhibit a beautifully re- 

 gular arrangement; whereas the so-called 

 pores of the author are totally devoid of 

 definite arrangement. 



BIBL. Keber, MikrosJc. untersuch. ub. die 

 Porositat d. Korper, and Phil. Mag. 1854. 

 pp. 287 and 370. 



POROUS STRUCTURES OF PLANTS. 

 What are ordinarily called porous tissues 

 in vegetable anatomy are described in ac- 

 cordance with their real nature under the 

 head of PITTED STRUCTURES. True pores 

 do, however, occur in the walls of vegetable 

 cells, from secondary or ultimate changes in 

 their character. They are seen in the cells 

 of the leaves of Leucobryum and Sphagnum 

 (see SPHAGNACE^E). Other regular orifices 

 are produced in the walls of the cells of 

 many of the zoospore-producing Confervas, 

 as Conferva, Cladophora, Enteromorpha, &c. 

 (see PI. 5). The wall of the sporangial cell 

 of Achlya presents analogous openings, and 

 according to Cohn, pores are produced in 

 the spore-cells of SPH^ROPLEA to admit 

 the spermatozoids. The pits and the inter- 

 stices between reticulated fibrous secondary 

 deposits are often changed into true holes in 

 old cells, but this is a result of decay of the 

 primary membrane ; it takes place very 

 early, however, at the contiguous ends of 

 SPIRAL-FIBROUS and PITTED CELLS, co- 

 alescing to form ducts, changing the septum 

 formed by the adjoining ends into a kind of 

 grating or irregularly torn diaphragm. 



BIBL. See the heads referred to in this 

 article. 



PORPHYRA, Ag. A genus of Porphy- 

 raceae (Florideous Algae), with an expanded, 

 membranous, shortly-stalked frond, com- 

 posed of a single layer of cells approximated 



