Guide to the study of insects and a treatise on those injurious and beneficial to crops, for the use of colleges, farm-schools, and agriculturists . ts of the legs. The ven-tral arcs, or protozoonites, subdivide into ventral and pleuralparts, which signalize the formation of the permanent ringsof the body. The authors figuresand statement show, * though hedoes not state the fact clearly,that development progresses fromeach end of the body towards thecentre, as we have shown * to bethe case in insects. Thus theposterior half of the body repeatsthe mode of development andgeneral form of the ante
Guide to the study of insects and a treatise on those injurious and beneficial to crops, for the use of colleges, farm-schools, and agriculturists . ts of the legs. The ven-tral arcs, or protozoonites, subdivide into ventral and pleuralparts, which signalize the formation of the permanent ringsof the body. The authors figuresand statement show, * though hedoes not state the fact clearly,that development progresses fromeach end of the body towards thecentre, as we have shown * to bethe case in insects. Thus theposterior half of the body repeatsthe mode of development andgeneral form of the anterior, orcephalic pole. The third period in the life ofthe embryo dates from the forma-tion of the ventral rudiments to the exclusion of the first change consists in the lengthening and meetingof the rudimentary legs. The mouth-parts develop this period the limb-bearing (pleural) region of thebody separates and the sternal piece or breast-plate appearsas a slower, later formation. Now the thoracic legs growmuch more rapidly than the mouth-parts and lie interlockedupon the breast. (Fig. G2G,t) When the first pair of legs are. Fisr. 626. * PropeediiiKs Boston Society of Natural History, Feb. 7, 626, m, mandibles; mx, maxilla;; /,4ouitli paii of legs; p, postabdomea 638 ARACHNIDA. long enough to cross each other the jointed structure of thelimbs disappears, and they soon become divided into theirusual number of joints, though the tarsal joints are the last tobe perfected. At this time the maxillae become differentiated,or split up, into the basal lobe and its appendage, or palpus,Claparede compares the basal lobe to the coxa of the legs,though it is formed long before the coxte of the feet them=selves. The anterior pair of appendages form the mandibles. The formation of the head is next in order. The cephaliclobe is divided into what the author calls two procephaliclobes, separated by a deep incision, and at this period thehead appears very distinct f
Size: 1389px × 1799px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1880, bookpublishe, booksubjectinsects
