STUDIES OS THE ECTOPARASITIC TEEMATODES OP JAPAN. 15I 



be regarded as a chitinised portion of the investing mem- 

 brane. This view Avil], as will be seen afterwards, unify the origin 

 of the chitinous hooks and rods that are found in various parts 

 of the body. 



The connective-tissue and chitinous penis of MonocoUjle seem to 

 me to afford a starting point for another type of copulatory organs, 

 that of the penis of Dididophom and Calicotijle. In the latter genus 

 (PI. XIX, fig. 11) the bulbous penis, or as it may be called the bulbus 

 copiilatorius'^, is a kidney-shaped mass of fibrous connective tissue 

 around the terminal portion of the vas deferens, before it is con- 

 tinued into the tubular chitinous penis. The latter is essentially 

 similar to that of Momcotijle, and is enclosed in the genital atrium 

 Avhich has here been reduced to a mere sheath for the chitinous penis. 

 The bulbus copulatorius may be regarded as a further differentia- 

 tion in a different direction of such penis as that of Monocotyle, in 

 consequence of which it has been almost completely separated from the 

 surrounding tissue. The only difference is that in Monocotyle it pro- 

 jects into the genital atrium, while in Calicotijle it does not, and is 

 therefore traversed by the vas deferens. The connective-tissue penis of 

 Diclidopliom (PL XI, fig. 4) is essentially similar in structure — ^histo- 

 logical details and the shape not considered — to that of Calico- 

 tijle. The chitinous penis is, however, replaced by the hooks already 

 described. These are also, in my opinion, formed by the local transforma- 

 tion of the lining membrane of the genital atrium, and are therefore 

 homologous in a broad sense to the chitinous penis of Calicotijle and 

 Monocotyle. Unlike, however, what occurs in these genera the lining 

 membrane has in Diclidopliom not been r<T.ised and prolonged into a 

 tubular form and the whole then changed into a chitinous substance, 

 but it has been raised at some particular points into the particular 



1). Braun— Warmer, p. 475. 



