. Outlines of zoology. Zoology. 58 REPRODUCTION AND LIFE HISTORY OF ANIMALS. special glands or glandular cells in the walls of the oviducts {, the " shells" of many eggs). The envelope is often firm, as in the chitinous coat around the eggs of many Insects, and in these cases there is often a little aperture (micropyle) through which alone the spermatozoon can enter. The hard calcareous shells round the eggs of Birds and Tortoises, or the mermaid's purse enclosing the egg of a skate are of course formed after fertilisation. Egg shells must be distinguished from egg capsules or co
. Outlines of zoology. Zoology. 58 REPRODUCTION AND LIFE HISTORY OF ANIMALS. special glands or glandular cells in the walls of the oviducts {, the " shells" of many eggs). The envelope is often firm, as in the chitinous coat around the eggs of many Insects, and in these cases there is often a little aperture (micropyle) through which alone the spermatozoon can enter. The hard calcareous shells round the eggs of Birds and Tortoises, or the mermaid's purse enclosing the egg of a skate are of course formed after fertilisation. Egg shells must be distinguished from egg capsules or cocoons, , of the earthworm, in which several eggs are wrapped up together. The Male Cell or Spermatozoon is a much smaller and usually a much more active cell than the ovum. In its. Fni. 8.—Forms of Spermatozoa (not (lra\\"n to scale). I and 2. Immature and mature spermatozoa of snail ; 3. of bird; 4. of man (//, head; w, middle portion ; ;", tail); 5. of salamander, with vibratile fringe (X); 6. of Ascaris, slightly amoeboid with cap (c); 7. of crayfish. minute size, locomotor energy, and persistent vitality, it resembles a flagellate monad, while the ovum is comparable to an amoeba or to one of the more encysted Protozoa. A spermatozoon has usually three distinct parts: the essential " head," consisting mainly of nucleus, and the mobile " tail" which is often fibrillated, and a small middle portion between head and tail, which is regarded by some as the centrosome. The spermatozoa of Threadworms and Crustaceans are sluggish, and inclined to be amoeboid (Fig. 8 (6, 7) ). Both ova and spermatozoa are true cells, and they are. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Thomson, J. Arthur (John Arthur), 1861-1933; Newbigin, Marion I. (Marion Isabel), 1869-1934; Smith, Pr
Size: 2162px × 1156px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
