134 A - RICHARDS. 



OBSERVATIONS. 



Morphological discussions are without the scope of this re- 

 search, but a knowledge of the derivation is helpful to an under- 

 standing of the development of the structures dealt with. Ex- 

 cluding the cuticle the writer has not given much attention to 

 the "ectoderm question," but his view, in so far as his observa- 

 tions warrant one, is that the cuticle also is of parenchymal 

 origin all of the adult structures of the tape-worm are derived 

 from the parenchyma. Parenchyma is physiologically similar to 

 embryon : c mesenchyme in that from it are derived muscle fibers, 

 flame cells, etc. The testes arise from the parenchyma first in 

 the region of the longitudinal excretory tubes and later appear 

 medianward, occupying the side of the worm commonly desig- 

 nated as dorsal. The animal is incompletely protandrous for 

 the ovaries arise later and many of the testes have completed 

 their development and degenerated before the female germ cells 

 have progressed very far. The last of them do not complete 

 their cycle until most of the ova have already been fertilized 

 but all ultimately degenerate and their place is taken by the 

 branches of the uterus. 



The first anlage of the female reproductive apparatus arises 

 also in the neighborhood of the excretory tubes and grows both 

 laterally and medianward. Its lateral growth gives rise to the 

 seminal receptacle and the vagina. Its median growth is the 

 beginning of the oviduct, which later branches to form the uterus, 

 of the vitellarium and shell glands, and of the ovary. Thus the 

 entire female apparatus arises from an originally single, indiffer- 

 ent anlage. This shortly differentiates into the separate anlagen 

 each of which from now on pursues its own individua' course. 

 That of the ovary is the innermost part of the original anlage. 

 It develops its investing membrane and begins a growth, due to 

 the growth of the germ cells composing it, which ends only when 

 the ova have all attained their complete size and developed the 

 needed amount of yolk. These in a rapid passage through the 

 oviduct are fertilized and enclosed in a thin shell. Maturation 

 is completed in the uterus where cleavage occurs and early 

 embryonic life is passed. When all of the ova have been fertilized 

 the reproductive mechanism except the uterus degenerates. The 



