52 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 



(2) The female organs consist of two convoluted tubes, ten 

 times the length of the body, which unite to form a short 

 unpaired section that opens to the exterior. 



Three regions are distinguishable in each tube, ovary, oviduct, 

 and uterus, while the unpaired part is a vagina. The ovary is ana- 

 logous in structure to the spermary, like it being traversed by a 

 rachis, from which in this case ova arise.. The mature ovum is of 

 ovoid shape, invested by a delicate vitelline membrane except at 

 one point (the micropyle), and consisting of vitellus (protoplasm) 

 with numerous contained yolk particles, nucleus (germinal vesicle), 

 and nucleolus (germinal spot). The wall of the oviduct contains 

 a muscle layer, and so does that of the much wider uterus, which 

 also possesses a lining raised into numerous longitudinal ridges. 

 The wall of the narrower vagina contains internal circular and 

 external longitudinal muscle-layers. 



Ascaris megalocephala presents special facilities for the study 

 of ovum-development (oogenesis) and fertilization, since a single 

 female specimen furnishes all the various stages. 



The sperms, ejected into the vagina, crawl by amoeboid move- 

 ments to the upper ends of the uteri, where they meet and unite 

 with the mature ova. In their upward course the sperms pass 

 along the grooves between the ridges into which the uterine 

 lining is raised, and so escape, being swept back by the descending 

 current of ova, The fertilized ova are surrounded by thick egg- 

 shells secreted by the glandular lining of the uteri, and also by 

 firm membranes developed within the shell by the oosperms 

 themselves. 



6. The Nervous System (Fig. 15) is made up of a ring, which 

 closely surrounds the anterior part of the gullet, and gives off 

 ill-defined longitudinal nerves, six in front and six behind. Two 

 of the former (the largest) run in the lateral lines, and the rest 

 near the median lines, one of the latter is dorsal, one ventral, 

 while the others are sublateral and do not extend far back. The 

 dorsal and ventral nerves are connected by a number of trans- 

 verse commissures. The circumoesophageal ring is somewhat 

 swollen at the origins of the lateral and ventral nerves to form 

 two lateral ganglia and a ventral ganglion. There is also a small 

 anal ganglion in front of the anus (or cloacal aperture). The 

 ganglion-cells are most abundant in these ganglia, but are not 

 limited to them. 



