Abstract
Summary. Vanessa urticx has six Malpighian tubules, three on each side which open into the colon by a common duct. Between the tubules proper and the common duct is a small‐celled undifferentiated region known as the imaginal ring or interstitial ring. The posterior ends of the tubules enter into close association with the wall of the rectum forming the rectal plexus. In the embryo (of Pieris hrassicse) the tubules arise in association with the proctodeum. During the first half of the embryonic period the tubules grow by active cell division, but there is no differentiation. During the second half of the embryonic period differentiation takes place, but no new cells are formed. In the larva (of Vanessa urticse) the tubules grow by an increase in the size of their constituent cells. The nuclei are rounded at first but become palmate and finally much ramified. The nuclei of the cells of the rectal plexus remain rounded throughout larval life. In no parts of the tubules proper is there any cell division. The common duct increases in size by a continuous enlargement of its constituent cells. There is no cell division. This mode of growth is similar to that of the hind‐gut. The interstitial (imaginal) ring continues cell division throughout larval life. As a formative region, however, it is relatively inactive and adds only a few cells to the tubules proper and common duct. It appears to be a relic of the embryonic blastopore, which fails to differentiate completely but retains to a slight extent its capacity for producing endoderm internally (tubules proper) and ectoderm externally (common duct).
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call