238 EMBRYOLOGY 



cord to the dorsal nerves of tlie Platjhelmintliee, and to 

 compare the lateral nerves of the latter to the two nerves of 

 the lateral lines in Nematoda. It must be noted, however, 

 that the facts actually established offer no certainty that 

 this comparison is justified. More uncertain still are the 

 observations on the further changes of the mesoderm. The 

 mesoderm cells multiply greatly, separate from the two cell- 

 rows, and migrate in various directions. They also penetrate 

 between the fundaments of the nervous system and the skin, 

 separating these from each other (Fig. 110^, mes). Finally, 

 the mesoderm forms a rather even layer between the in- 

 testine and the epidermis, so that the originally bilateral 

 arrangement thus disappears. It would be important to 

 know more accurately about the formation of the body cavity 

 in the Nematoda. 



The origin of the sexual organs, which in the early stages 

 is the same for both sexes, is better known. In each of the 

 mesodermal bands, which at first consists of only a few cells, 

 one of these cells is distinguished by its remarkable size 

 (Fig. 110 D and E, g). It constitutes the fundament of the 

 genital organs. In Bhahditis a cord of cells is developed 

 from it by division, the individual elements of which divide 

 further, and finally become the sexual products (Goette). 

 In other Nematoda the original cell multiplies, it is true, but 

 the protoplasmic bodies of the newly formed cells do not 

 separate from one another ; on the contrary, a syncytium with 

 many nuclei is formed. The sexual fundament, which is at 

 first saccular, grows and differentiates into germ glands and 

 ducts. While in the former the protoplasmic mass with the 

 nuclei persists as the germarium, in the latter a peripheral 

 epithelium is formed (Ant. Schneider). 



The shape of the ripe embryo resembles on the whole that 

 of the Nematode, although it still has to undergo, especially 

 in the parasitic worms, many changes before it attains the 

 adult form. Several moultings are often necessary for this. 

 In some cases the embryo possesses provisional organs, which 

 appear to be adaptations to its mode of development. Thus 

 in ISpiroptera obtusa and Cucullanus elegans a boring-tooth is 

 found at the edge of the mouth, and the posterior end of 



