DESCEIPTION OF THE ENGKAVINGS. 955 



26 b. from the lateral surface ; two bands of clilorophyll are seen on each side, and their 

 section at the angles ; 26 c. from the base ; 27. Seen from below, nucleus with nucleoli 

 and sap-currents; lai-ge and small clilorophyll-globules ; Zl b. Seen from the side; the 

 two lateral bands of chloropliyil are seen, and a parietal nucleus, with sap-currents from it, 

 in the centre of one side ; 27 c. An individual after division, seen from the side. The 

 chlorophyll bands appear only in section. Each secondary cell has a parietal nucleus. 

 28 a, h, c, d. Bacillaria Nageli : a, viewed from the broad side, a granidar nucleus in the 

 centre ; b, also the broad side, an individual before division, the nucleus primarily divided ; 

 c, division complete ; d, viewed from the base (in section). 29 a, b, c, d. Melosira Dickieii 

 (Thwaites) : a, filament, in ordinary state ; b, filament, the terminal cells of wliich are 

 becoming converted into sporangia ; c, sporangia ; d, sporangial frustides becomuig deve- 

 loped from one of the halves of a previously divided sporangium, X 220. 30 a, b. Mas- 

 togloia Danseii (Thwaites) : a, portion of frond, X 35 ; b, a part of same, X 220. In it 

 two frustales are shown, one in front, the other on side aspect. 31 a, b, c, d. Dickieia 

 ulvoides (Ralfs) : a, natural size, in different stages of growth ; b, frustules (navicular 

 bodies) higiily magnified when fresh ; c, one when dried ; d, a lateral view of the same ; 

 e, a portion of frond, less highly magnified, showing the simple and binate frustules. 



32. Melosira varians (Thwaites) ( = Grallionella, Ehr.), filament with sporangia, X220. 



33. M. Italica, filament with sporangia. 34. Dictyocha Fibula. 35. D. trifenestra. 



PLATE XVI. (Diatoms and Desmids). 



Figures 1 to 6. Navicula (Pinnularia, Eln-.) major. Erom Schleiden's ' Principles of 

 Botany,' to illustrate the structiu'e of the silicious valve. 1. s. v. (venter, Ehr.). " In the 

 middle line are two clefts, terminating at the centre, as well as at the other ends, with a 

 little ch'cular enlargement, more clearly seen in figs. 3 and 5. The rounded spot in the 

 middle, and at the two ends, is not a hole as represented by Elu-enberg. That such a hole 

 is decidedly sometimes not present, is seen in such fragments as figs. 3 and 5. In the 

 position of the oblique lateral clefts (striae or costae, Elu-.), the valve consists of two leaves, 

 penetrated by tlae clefts, which, where both the lamellae touch each other, are somewhat 

 broader, which explains the varying breadth of the clefts according to the alteration of the 

 foci. Fragments in which tliis structm-e is clearly represented may be frequently obtained 

 by crushing the valve (fig. 6). 2. A front view, showing that the rounded enlargements of 

 the median line are but depressions on the external surface. The double contom-, denoting 

 the thickness of the wall, is well seen. Tliis clearly shows that a passage exists from the 

 top to the bottom of the valve, wliich may be easily confu-med if the valve, or better still an 

 oblique section of it, be looked at from above ; fig. 5 is su.ch a section." 7, 8. Cymato- 

 pleura elliptica (Smith). 9. C. Solea. 10-19. Ciosterium Ehrenbergii (Smith), showing 

 the stages in its conjugation, and the formation of the sporangia: 10. A single frond in its 

 ordinary condition ; 11. Two fronds approaching to conjugate ; 12. Conjugating fronds 

 undergoing self-division, the upper showing the protuberances through the torn apices of 

 which the contents of the divided fronds pass into the sporangia ; 13. Shows the passage of 

 the endoclu'ome-sac and its contents ; 14. Conjugated fronds having perfected then* spo- 

 rangia; 15 (after M. Morren). Development of the "propagules" into yomig fronds; 

 16, 17, 18, 19 (from Morren). Development of a sporangium into a Ciosterium with 

 unequal segments: the figures are all mag-nified 100 times. 20-26. Surirella biseriata 

 (Smith). To illustrate the structure of the valve and self-division of the frustule : 20. View 

 of frustules on the completion of self-division ; 21. Apertures of costal canals seen in front ; 

 22. Silex of connecting membrane after maceration in acid ; 23. f. v. (the broad median 

 longitudinal band is the connecting zone of the two valves) ; 24. s. v. ; 25. e. v, ; 26. 

 Transverse section of empty frustule. 



PLATE XVII. (Diatoms and Phytozoa). 



Figures 506-509. Pyxidicula globata. 511 & 515. Xanthidium ? ramosum. 512. 

 X. hirsutum. 513, 514. X. ? difforme. 516-518. Cainpylodiscus ClyiJcus. 519-531. 

 Spirillum Bryozoon. 532, 533. Astasia navalis. 534. G-yges sangmneus. 



PLATE XVIII. (Phytozoa). 



Figure 1. MonasCrepuscidum, x800. 2. Monas Punctum. 3,4. Uvella Glaucoma, 

 X 350 : 4. Detached monads, 5. Polytoma Uvella. 6. Microglena monadina. 7. Gle- 



