138 



ENTOZOA. 



slightly wavy line to near the middle of the 

 posterior margin of the segment, where it ter- 

 minates in a small oval vesicle. This, as seen 

 by transmitted light, is sub-transparent in the 

 centre and opaque at the circumference, indi- 

 cating its hollow or vesicular structure. The 

 duct, or vas deferens, contains a grumous se- 

 cretion ; it is slightly dilated just before its 

 termination. 



In this species therefore, as also in Amphis- 

 torna conicum, the ova are impregnated in their 

 passage outward. But in several species of 

 Distomata, as D. clavigerum, ovatum, cirrige- 

 runij and in the Distoma hepaticum, the ova 

 escape by an aperture situated near the base of 

 the penis, and reciprocal fecundation exists. 

 The concourse of two individuals must also take 

 place in those species of the genus Monos- 

 tomum, which, like the Monostomum mutabile, 

 are viviparous, and in which the orifices of the 

 male and female parts are distinct. 



All the Sterelmintha of the Trematode order 

 are androgynous; but the generative apparatus, 

 instead of being divided and multiplied as in 

 the Tania, is individualized, and its several 

 parts receive a higher degree of development. 

 We have selected the figure which Nordmann 

 has given of the Distoma perlatum, on account 



Fig. 91. 



Generative organs, Distoma perlatum, magnified. 



of the clearness with which the several parts 

 are delineated, but it must be observed that it 

 deviates in some remarkable peculiarities from 

 what may be regarded as the Trematode type 

 of the reproductive organs. 



The specimen is seen from the under side, 

 part of the parietes of the body having been 

 removed ; a is the oral aperture, b the oesophagus 



seen through the transparent integument, c d 

 the windings of the beginning of the simple 

 digestive cavity, e e the two intestinal prolon- 

 gations, //' the dilated claviform co2cal ter- 

 minations of the intestines, g the two internal, 

 and h the two external trunks of the vascular 

 system proceeding to the anterior part of the 

 body; i is the great sacciform uterus, k ap- 

 parently glandular bodies contained therein, 

 / m the two testes, which are beset internally 

 with small spines or cilia; n the projecting 

 cirrus from which the ova are expelled, o the 

 terminal dilatation of the oviduct which com- 

 municates with the testes, p p p p convo- 

 lutions of the oviduct which are filled with ova, 

 q q the mass of ova which lies above the ovi- 

 duct, and occupies almost the whole cavity 

 of the body, r r the passages by which the 

 ovaries communicate with the uterus or dilated 

 commencement of the oviduct. 



The generative organs present some varieties 

 in the Planarite, but are essentially the same 

 as in the Distomata. In the Planaria lactea 

 the penis and oviduct are situated below, and 

 the two vesicular and secerning parts of the 

 apparatus towards the upper part of the body. 

 The male organ (a, fg. 92) consists, according 



Fig. 92. 



to the researches of Professor Duges, of two 

 parts, one of which is free, smooth, semi- 

 transparent, contractile, and always divided 

 into two portions by a circular constriction ; 

 it is traversed by a central canal, susceptible 

 of being dilated into a vesicle, and is open at 

 its free extremity, which is turned backwards ; 

 the second division is thicker, more opaque, 

 vesicular, adherent to the contiguous paren- 

 chyma, and receives two flexuous spermatic 

 canals (6, 6). The free portion of the penis is con- 

 tained within a cylindrical muscular sheath (c), 

 which is adherent to the circumference of the 

 base of the intromittent organ, and serves to 

 protrude it externally. This sheath commu- 

 nicates with the terminal sac of the female 

 apparatus near its outlet by a projecting orifice 

 (of). The oviduct (e) opens into the posterior 

 part of the terminal sac : it is a narrow tube 

 which passes directly backwards, and dividing 

 into two equal branches, again subdivides and 

 ramifies amongst the branches of the dendritic 

 digestive organ. Besides the ovary there are 

 two accessory vesicles (gand//), communicating 

 together by a narrow duct (f), and opening 

 into the terminal generative sac. 



M. Baer twice witnessed the copulation of 



