. Elementary text-book of zoology, general part and special part: protozoa to insecta. Animals. OEPIITEEA. , 391 posterior segmental organs (anal vesicles, lig. 314, Ah) in the terminal segment, each of which has a number of peritoneal funnels and opens into the rectum. In Bonellia the segmental organ which performs the function of uterus is, like the ovary, sin^e (fig. 314 6). Development.—The development of the ovum begins witli an unequal segmentation. In Bonellia the small ceils of the animal pole grow round the four large yolk spheres, which give rise to the entoderm, leaving a
. Elementary text-book of zoology, general part and special part: protozoa to insecta. Animals. OEPIITEEA. , 391 posterior segmental organs (anal vesicles, lig. 314, Ah) in the terminal segment, each of which has a number of peritoneal funnels and opens into the rectum. In Bonellia the segmental organ which performs the function of uterus is, like the ovary, sin^e (fig. 314 6). Development.—The development of the ovum begins witli an unequal segmentation. In Bonellia the small ceils of the animal pole grow round the four large yolk spheres, which give rise to the entoderm, leaving a small aperture, the blastopore (fig. 110). The EcMurus (fig. 315) are the most accurately knoAvn. They present the type of Loven's larva and possess a strongly developed. Fig 315 -a Larva of Eclnurus from flie ventral side (after Hatschek). SP, apical plate j 'prw pv£eoral circle of cilia; Pov^, postoral circle of cilia; i-»,head-kidney; , ventral r-an-lionic cord connected with the apical plate by the long oesophageal commissures ; AS "anal vesicle. 6, Ventral region of the Echiiivns larva with segmented mesodermal bands; SC, oesophageal commissure; Dsp, dissepiments of the anterior body segments; 2IS, mesodermal bands ; A, anus. prteoral circle of cilia {Prio), in addition to which there is also a delicate post-oral circle of cUia {Pow). Early in larval life a seg • mental organ, the head kidney or pronephros {KN), is developed, one on either side; and behind it a pair of mesoblastic bands makes its appearance and gives rise in the subsequent development to the rudiments of 15 segments (fig. 315 h). In the terminal segment, which is surrounded by a circle of cilia, there appear segmental. 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 Claus, Carl, 1835-1899; Metcalf Collection (North
Size: 2044px × 1223px
Photo credit: © Paul Fearn / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, booksubjectanimals, bookyear1892
