. Occasional papers of the California Academy of Sciences. C tarsus of mesothorocic leg Figure 17. A. Prothoracic leg. B. Mesothoracic leg. andC. Its Rgure 18. External aspects of foretarsus of a female. According to Earths excellent cytologicai inves-tigation—the first made with the aid of an electronmicroscope—the silk-ejectors and their glands areunique organs. As shown in my diagrammed hypoth-esis (Fig. 19A), the glands perhaps evolved from in-vaginations of secretory cell pores in the silk-ejector apparently represents a setae-like,evagination of the exocuticle wh
. Occasional papers of the California Academy of Sciences. C tarsus of mesothorocic leg Figure 17. A. Prothoracic leg. B. Mesothoracic leg. andC. Its Rgure 18. External aspects of foretarsus of a female. According to Earths excellent cytologicai inves-tigation—the first made with the aid of an electronmicroscope—the silk-ejectors and their glands areunique organs. As shown in my diagrammed hypoth-esis (Fig. 19A), the glands perhaps evolved from in-vaginations of secretory cell pores in the silk-ejector apparently represents a setae-like,evagination of the exocuticle which might first havebeen simply a cuticular rim around a pore opening. It is probable that the early ectodermal glandswere hollow balls composed of walled secretorycells. The duct, or constriction, leading to each pri-mordial silk-ejector must at first have been fully cell-lined. The inner walls of these duct cells appear tohave gradually thickened and fused to become theelaborate ducts which now extend from the silk glandsto the ejectors. Similar ectodermal glands are treat-ed and illustrated by Snodgrass (1935: 62, fig. 32). Cells of the ectoderm
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectscience, bookyear1890
