An introduction to the study of the comparative anatomy of animals . oducts,constituting the male and female pronuclei, are pushed into thebody of the macrogamete, where they fuse together to form acombination nucleus. As soon as the fusion is complete the water collected beneaththe peristome of macrogamete is ejected, the protoplasm movesforward to take its place, carrying with it not only the com-bination nucleus but also the protoplasmic contents of themicrogamete. The latter is now reduced to a mere membranousappendage, which shrivels up and eventually falls off and is lost. Digitized by M
An introduction to the study of the comparative anatomy of animals . oducts,constituting the male and female pronuclei, are pushed into thebody of the macrogamete, where they fuse together to form acombination nucleus. As soon as the fusion is complete the water collected beneaththe peristome of macrogamete is ejected, the protoplasm movesforward to take its place, carrying with it not only the com-bination nucleus but also the protoplasmic contents of themicrogamete. The latter is now reduced to a mere membranousappendage, which shrivels up and eventually falls off and is lost. Digitized by Microsoft® CONJUGATION OF VORTICELLA 213 The combination nucleus soon elongates to form a fibrousspindle, and divides by mitosis. Two more divisions follow, sothat the macrogamete contains eight similar nuclear of these does not grow any further, but assumes the char-acters of a micronucleus. The other seven become spherical,and grow rapidly till each consists of a central mass of granularmatter separated by a clear space from a well-defined nuclear. Fig. 46. Diagram of the course of conjugation in Vorticella jjtotiilaia, constructed on thesame principle as fig. 43, which should be compared. (After Maupas.) membrane. The fertilised macrogamete, if well fed, is nowready to divide. The large corpuscles, which may now becalled macronuclei, do not divide, but are distributed to theoffspring, four passing into one and three into the other of thetwo individuals resulting from the first division. The micro-nucleus, on the contrary, divides, one of its products passinginto each of the daughter Vorticellae. The rest of the processhas not been determined with absolute certainty, but it is Digitized by Microsoft® 214 COMPARATIVE ANATOMY probable that it follows the course indicated in the diagram,fig. 46. The young Vorticellid with four macronuclei under-goes two more divisions, each accompanied by a division ofthe micronucleus, whilst macronuclei are simply distributedequ
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