. A textbook of invertebrate morphology [microform]. Invertebrates; Morphology (Animals); Invertébrés; Morphologie (Animaux). and Polyphemus, the branchial lobes being at the same time rudimentary or entirely wanting. The abdomen, which is composed of four segments, possesses on its dorsal surface elevations for the closure behind of the brood-chamber, and on its terminal segment set* are usually developed; it does not, however, bear any appendages. The heart is an oval structure situated in the thoracic re- gion and possesses but a single pair of ostia. The lateral eyes are in all cases fused
. A textbook of invertebrate morphology [microform]. Invertebrates; Morphology (Animals); Invertébrés; Morphologie (Animaux). and Polyphemus, the branchial lobes being at the same time rudimentary or entirely wanting. The abdomen, which is composed of four segments, possesses on its dorsal surface elevations for the closure behind of the brood-chamber, and on its terminal segment set* are usually developed; it does not, however, bear any appendages. The heart is an oval structure situated in the thoracic re- gion and possesses but a single pair of ostia. The lateral eyes are in all cases fused to form a double eye situated in the median line of the head and capable of movement within a socket by means of muscles which are attached to it. The majority of the Cladocera jiro fresh-water forms, though some, such as Evcuine, are marine. The ova undergo development in a brood-chamber formed by the space in- cluded between the shell-valves and the dorsal surface of the abdomen, and in Evadne and Polyphemus, as already stated, the entire shell, which is somewhat reduced in size, is adapted to serve as walls for the chamber. As in the Branchiopoda, collections of Cladocera, es- pecially if made during the spring or summer, will show an enormous preponderance of females, and several generations may be reared without a single male making its appearance. The eggs, which have a thin egg-membrane and little yolk, develop parthenogenetically and produce females, and this method of reproduction will continue so long as the condi- tions, such as temi)erature and food, remain satisfactory; hence the eggs of this kind are generally known as " summer ; Towards autumn, however, or whenever the condi- tions tend to become unfavorable, males, distinguishable by their smaller size, the absence of a brood-pouch, and their more highly-developtu! sn^ns- organs, as well as by the de- velopment of hooked setie on the anterior appendages wliicli serve as clasping organs, make th
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Keywords: ., bookcentury1800, bookdecade1890, bookpublishernewyo, bookyear1896
