Outlines of zoology . supra-oesophageal ganglion in the h«ad, a sub- ROTATORIA. 24S oesophageal about the middle of the body, long commissures betweenthem, and numerous nerves from both; it retains its primitive con-nectioii with the epidermis. There are two eyes and various patchesof sensitive cells. The food canal is complete and simple, and lies in aspacious ciliated body cavity. Corresponding to the external divisions,the cavities-of the head, body, and tail are distinct, being separatedfrom one another by septa; a longitudinal mesentery supports the ^utand divides the cavities into latera
Outlines of zoology . supra-oesophageal ganglion in the h«ad, a sub- ROTATORIA. 24S oesophageal about the middle of the body, long commissures betweenthem, and numerous nerves from both; it retains its primitive con-nectioii with the epidermis. There are two eyes and various patchesof sensitive cells. The food canal is complete and simple, and lies in aspacious ciliated body cavity. Corresponding to the external divisions,the cavities-of the head, body, and tail are distinct, being separatedfrom one another by septa; a longitudinal mesentery supports the ^utand divides the cavities into lateral halves. There is no vascular system, nor are there any certain nephridia. Itis possible that the latter may be represented by the genital ducts. The animals are hermaphrodite, and the simple reproductive organslie near one another posteriorly. The two ovaries project into thebody cavity, and their ducts open laterally where body and tail two testes project into the cavity of the tail; and their ducts have. Fig. 126.—Development of Sagitta.—After O. forination of a body cavity by pocketsfrom the archenteron; also the early separation ofreproductive cells. .£c.,, Ectoderm ; En.^ endoderm ; ac.^ archenteron; R., repro-ductive cells; bl.^ blastopore; ^ ccElom pouches; /«.,mouth; I. section of gastrula; 2 and 3. origin of coelompouches. internal ciliated funnels, and open on the tail. Two reproductive cellsare set apart at ». very early stage, and each divides into the rudimentof an ovary and of a testis. The eggs undergo complete segmentation;a gastrula is formed by the invagination of the blastula; the bodycavity arises, in enteroccelic fashion, as two pockets from the arch-enteron. The young forms are like the adults. Appendix (2) to Annelid Series Class Rotatoria. Rotifers Rotifers are beautiful minute animals, abundant in fresh water, alsofound in damp moss, and in the sea. They owe their name and theold-fashioned title of wheel-anim
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Keywords: ., bookcentury1900, bookdecade1910, bookidcu3192, booksubjectzoology
