174 Mr. H. J. Carter on the Conjugations of some Diatomece. 



nature of ovules, I cannot divest myself of the idea that they 

 are produced by some ovarian organ. 



But, from what has been stated respecting the glair-cell in 

 the Diatomeae, it seems to me not impossible that this may be 

 the organ which here supplies the germ — and not the sperm-cells, 

 as supposed by Ehrenberg. 



EXPLANATION OF PLATE IV. 



N.B. All the figures in this plate are drawn upon the scale of -(Vth to 

 , ;o \) th of an inch, together with most of their detail. 



Fig. 1. Navicula serians, Kg. In conjugation, showing formation of the 

 spore or sporangium : a a, the pellicle of the gelatinous secre- 

 tion in which the conjugating frustules first imbed themselves; 

 b, b, valves of the two conjugating frustules ; c, spore or sporan- 

 gium ; d, dark shade representing endochrome ; e, circles repre- 

 senting oil-globules. 

 (After this the same parts will be indicated by the same letters, 

 where it seems desirable to insert them.) 



Fig. 2. The same. The spore divided into two equal portions, each spheri- 

 cal, and surrounded by the capsules,/,/, respectively, as indicated 

 by the white interval which separates the dark shade or endo- 

 chrome from the margin. 



Fig- 3. The same. The capsules divided in their equatorial lines respect- 

 ively, and their hemispheres separated for some distance by the 

 sheaths of the sporangial frustules, g, g, on which the rings of 

 their more advanced development are not visible, even if formed. 

 The conjugating frustules absent. 



Fig. 4. The same. Still more advanced state. The rings on the sheath h 

 now visible ; h', the other half of the spore abortive. 



Fig. 5. The same. Still more advanced stage ; the rings omitted on the 

 sheath which lies inferiorly. 



Fig. 6. The same. Still more advanced stage : i, the interval between 

 the rings in the centre of the sheath. 



Fig. 1 . The same. Still more advanced stage. The undermost half or 

 sheath not seen. Shows the ends of the capsule beginning to 

 disintegrate, /, /. 



Fig. 8. The same. Still more advanced stage. The ends of the capsules 

 disintegrating into short, fusiform, curved, thread-like fibres,/,/. 



F'uj. 9. The same. Fully formed sporangial frustule, as seen within its 

 sheath. 



Fig. 10. The same. Empty sheath, showing the longitudinal fissure of 

 dehiscence. 



Fig. 11. Navicula rhomboides, Ehr. In conjugation. The pellicle of the 

 gelatinous secretion and the ends of the capsules absent. 



Fig. 12. The same. More advanced stage. 



Fig. 13. The same. Fully formed frustule. Appears broader than the 

 pair of sheaths in fig. 12, probably because their narrow, and not 

 their broad, surfaces are seen. The dark shade on the frustule, 

 which consists of transverse parallel lines, is thus seen under a 

 magnifying power of 800 diameters. 



Fig. 14. The same. Smaller individuals in conjugation, the valves of the 

 conjugating frustules having a terminal rather than a lateral 

 position as in the larger conjugations. 



