33] PROTEOCEPHALIDAE — LA RUE 33 



but little larger than the embryo. The third or inner membrane is a 

 delicate but tough and clear membrane which is not always easy to 

 demonstrate. It is closely applied to the embryo and might readily be 

 overlooked. 



CHARACTERS OP DIAGNOSTIC VALUE 



Benedict (1900:339) in his discussion of these forms called at- 

 tention to the small dependence that can be placed upon external meas- 

 urements when used alone as a means of determining species. While in 

 the main he is correct in his contentions it is certainly a fact that such 

 measurements when used in conjunction with other data may be of 

 great v^e and these should always form a part of the species descrip- 

 tion.[/These measurements should include the dimensions of the head 

 and suckers, the length of the strobila and its breadth at intervals or 

 the breadth of proglottids at certain stages of development. The dimen- 

 sions of proglottids are always of service, and of less importance are 

 the dimensions of the neck. Data as regards the host, the locality and 

 the habitat of the host are always of value. The older investigators made 

 much of these data and justly so for they were unable to make a study 

 of the internal anatomy of cestodes. At the present time such data do 

 not seem to be as highly valued as they should. The anatomy and finer 

 structure of the internal organs furnish the most valuable characters for 

 diagnostic purposes. The relations of the external genitalia, of the 

 male and female reproductive organs to each other, the number and size 

 and distribution of the testes, character of the coils of the vas deferens, 

 size and character of the cirrus-pouch, cirrus, ductus ejaculatorius, and 

 the protruded cirrus are all of value for diagnosis. So also are the 

 relations of the various parts of the vagina, the vitellaria, ovary, oviducts 

 and all of the small oi^gaiis-of the tfrterovarial space. Of especial value 

 are data in regard to the pouches of the uterus and the measurements 

 of the egg membranes and the embryo. The presence of muscular 

 elements and cilia may at times be used as distinguishing features. 

 Drawings showing the essentials of external and internal anatomy should 

 always form a part of a report on these animals. 



