No.nos. rROCEEBINGS OF THE NATIONAL MUSEVM. 205 



studied further when proper material is found. It is, however, by no 

 means tlie on]}" case of lioinoplasy brought forward in hehninthology. 

 I ]iave' elsewhere called attention to the branching of the intestine 

 in two distinct types of Hakes, as represented by Fasciola hejxdiac and 

 Diiitomuin delphini. The i:)resence of more than two testicles, as in 

 two or more other distinct types of flukes represented by VJeorchis 

 polyorchis and P. mollis on the one hand and THstomum ci/</noiih's or J). 

 ricJtardi on the other is, in my opinion, another case of homoplasy. 

 The development of double- pored forms in two distinct families (the 

 Bothriocephalidii^ — Blanchard's genus Krahbea, and a number of cases 

 in which a few double-ixn^ed segments have been found in Bofhrio- 

 cephalus latun — and the Ta'niidie forms a fourth case of the same nature. 



One of the greatest criticisms upon the present classification of para- 

 sites seems to me the fact that systeniatists have not taken into con- 

 sideration the principle so well established in paleontology and other 

 branches of zoology, namely, that the same structure may develop 

 independently in several parallel series of animals. The sooner this prin- 

 ciple is acknowledged the sooner we shall have a natural classiticatiou. 



Zone of lateral groiciJi. — A comparison of the older and younger seg- 

 ments of numerous Taniiidte shows that as the segments grow broader, 

 the median field — namely, the space between the two ventral canals — 

 increases nundi more rapidly in ]n'oportion than the lateral fields — 

 namely, the space between the ventral canals and the lateral mar- 

 gin. This establishes tlie median field as the greatest zone of lateral 

 growth. No particular narrow zone of the median field can be looked 

 upon as the zone of lateral growth for all cestodes, as is shown by a 

 comparison of a large number of forms. In Tauiia (type T. solium), 

 for instance, the entire median field appears to participate in a more or 

 less uniform lateral growth, for tlie genital glands retain their rela- 

 tive position, increasing in size in proportion to the increase in size 

 of the segment; the same a])pears to hold for Darainea. In the 

 auoplocephaline forms we find some interesting variations in the zone 

 of growth, as is shown by the relative position of the ovaries to the 

 ventral (canals or to the median line. In Thysanosoma (jiardi the ovary 

 bears an almost constant relation to the ventral canal, while the dis- 

 tance between the (»vai y and the median line constantly increases as the 

 segment grows broader ; in this case, therefore, there is but little growth 

 between the ovary and the canal, while the growth in the median side 

 of the ovary is very marked. The same holds true to a lesser degree 

 in Bcrtia ainericana. In Moniezia cjcpansa and M. planissima also the 

 relation of the ovaries to the ventral canals remains almost constant, 

 while the chief zone of growth is in the median field between the 

 ovaries. 



'The anatomy of tlie large American fluke (Fasciola maf/na) autl a comparison 

 with other species of the genus Fasciola s. st. vide p. 221, Jour. Comp. Med, Vet. 

 Arch., 1895. 



