154 CHILD. 



number of the testes frequently occurs in proglottids of less than 

 normal size. 



This brief review of these cases only serves to call attention 

 once more to the fact that was repeatedly pointed out in Parts I., 

 and II., viz., that the form and arrangement of the reproductive 

 organs may vary widely in correlation with variations in form of 

 proglottid. 



In case the form-variation is extreme, however, parts of the 

 reproductive organs may remain undeveloped and these parts 

 may be those which are essential for the normal functioning of 

 the system. The consideration of these cases leads to the very 

 important conclusion that the development of each part of the 

 reproductive organs shows a very close correlation with the de- 

 velopment of the particular region of the proglottid in which it 

 lies. This was pointed out repeatedly in Parts I. and II., and it 

 is not necessary to go over all the particular cases again. 



The different conditions represented are manifold. Apparently 

 any portion of the organs may fail to appear as this or that por- 

 tion of the proglottid fails to develop fully. In case the dorsal 

 side of the proglottid is distinct and the ventral is not, only the 

 vas deferens and testes appear, these lying in the dorsal region 

 of the proglottid (Figs. 16, // ; 17, //, etc., Pt. I.). If the ventral 

 side only is distinct from the adjacent proglottids only the female 

 organs or parts of them appear (Y. g., Fig. 22, d, Pt. I.). Ovary, 

 testes, and, in some cases, the inner portions of the vas deferens 

 and vagina ' may be present, but if the marginal region is dwarfed 

 the middle, or terminal portions, or both, of the ducts may be 

 entirely absent, or present only in part (c. g., Fig. 39, />, Pt. II.). 

 And finally, in extreme cases the reproductive organs may be 

 represented only by one or two small groups of cells in the region 

 where the ovary or vitellarium would appear if present (Fig. i8> 

 Pt. I.). 



It is rather common in cases of this kind to find a marginal 

 pore and perhaps the cirrus present but entirely unconnected with 

 the inner portions of the reproductive organs. Either the ducts 



'In Parts I. and II. the designation "oviduct" was incorrectly applied to the 

 whole female duct, including the vagina. Of course the oviduct proper is only a 

 small portion of this. I do not think that my use of the word was such as to cause 

 confusion in this particular case, but I desire to call attention to the error. 



