. Zoology : for students and general readers . Zoology. DEVELOPMENT OF SPONGES. 45 pears which may be seen through the body-walls. At this time the germ consists of two layers, the inner layer of cili- ated cells (endoderm) forming a closed sac, enveloped in the spiculiferous layer. Such are the observations of Metschni- kofE on the development of Sycon. According to the ob- servations of Barrois, the larva or gastrula fixes itself by what are destined to be the ectodermal cells, and which are the round non-ciliated cells forming the posterior end (Fig. 31, G) of the free-swimming gastrula. Ab
. Zoology : for students and general readers . Zoology. DEVELOPMENT OF SPONGES. 45 pears which may be seen through the body-walls. At this time the germ consists of two layers, the inner layer of cili- ated cells (endoderm) forming a closed sac, enveloped in the spiculiferous layer. Such are the observations of Metschni- kofE on the development of Sycon. According to the ob- servations of Barrois, the larva or gastrula fixes itself by what are destined to be the ectodermal cells, and which are the round non-ciliated cells forming the posterior end (Fig. 31, G) of the free-swimming gastrula. About this time the mesoderm separates from the endoderm, either before or just after the gastrula becomes stationary, according to the group to which it belongs. When the young sponge becomes stationary it does not differ from the gastrula, except that it becomes more or less. Fig. 31.—Development of a sponge {Sycon cUiatttm).—Afti^r MetechnLkoff. irregular in form. Then appear the food or digestive cavi- ties in the endoderm, in Sycanclra becoming radiating tubes lined with ciliated, collared, monad-like cells ; or in Leucon and Halichondria, and their allies, forming scattered pock- ets, called " «?ttp«.Zteceo?«.s ; Inmost sponges (except some calcareous species) there is no general body-cavity in the gastrula, nor in the young after the larva becomes sta- tionary, according to Barrois. After the formation of the ampullaceous sacs the pores open through the mesoderm and connect the sacs and ciliated channels, as the case may. 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 Packard, A. S. (Alpheus Spring), 1839-1905. New York : Henry Holt
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectzoology, bookyear1879
