120 



THE HELMINTHES. 



<^115. 



the genital organs of the first is yet imperfectly known ; while that of those 

 of the second is well understood. The female apparatus of the Tremato- 

 des consists of a germ-forming organ (ovary), with its excretory duct; 

 then, two others lor forming the vitellus, which have also excretory 

 ducts; and then a simple uterus with its vagina. The male apparatus con- 

 sists of testicles with their excretory canals, an internal seminal vesicle, a 

 cirrhus-sac, an external seminal vesicle, and a penis.*-' 



The ovary consists of a round or pyriform ''^^ reservoir, situated, usually, 

 upon the median line of the body,'"** from which it is distinguished by its 

 pale color and transparency. It is filled with simple round cells — the 

 egg-germs. The nucleus of these cells is the germinative vesicle, and the 

 nucleolus, the germinative dot.''^' 



The short and small excretory duct of the ovary opens at the commence- 

 ment of the uterus. The organs which secrete the vitellus are two in num- 

 ber, of variable length, and situated upon each side of the body near the 

 dorsal surface ; they occupy either the cervical, the central, or the posterior 

 portion of the animal, and sometimes extend over them all. They are 

 nearly always composed of ramified caeca filled with white, granular, 

 vitelline corpuscles. By reflected light these caeca appear through the 

 skin as a white, ramified, botryoidal mass,**^' and from each of them, pass 

 off inwardly, numerous excretory ducts, which reunite opposite the ovary 

 into two common canals. These last approach each other transversely, 

 and form a single canal upon the median line, which, after a short course, 

 opens at the bottom of the uterus by an orifice which is common to it and 

 the ovary,"'' • 



Pentastomum taenioides, organs which are re- 

 garded by Diesin^ as caeca for secreting the en- 

 velope of the eggs. 



Since all the parts of the genital organs of Pen- 

 tastomum have not been examined with tliis same 

 precision, I can give no opinion as to their use.* 



2 See Siel/old, in H'iesmann's Arch. 1836, I. p. 

 217, Taf. VI., and in Midler's Arch. 1836, p. 232, 

 Taf. X. fig. 1. 



3 The ovary here is always smaller than the 

 testicle, and sometimes as to form very closely 

 resembles it, as in Distomum globiporum, and 

 longicolle, milii (from the m-inary bladder of 

 Cottux s:obio) ; consequently it may easily be 

 taken for a third testicle. 



•* With MonostoTtium, it lies wholly at the pos- 

 terior extremity. 



5 In Polystomum, Octobothrium and Diplo- 

 zoon, the germs are so large that they may easily 

 be taken for perfect eggs. 



There is here, moreover, between the cell-wall 

 and the nucleus (the germinative vesicle), quite a 

 thick layer of albuminous substance, somewhat 



representing a vitellus. But in tlie other Trema- 

 todes it is so thin as scarcely to be perceived. 



6 With the following Trematodes there is a wide 

 deviation from this usual arrangement. In Dis- 

 tomum lonsicolle the organs producing the 

 vitellus are two simple round caeca located behind 

 the ventral sucker ; in Distomum cysnoides, 

 they are two very small deeply-fissured bodies ; 

 and in Distomum gibbosum, there is one only, 

 which is star-shaped and located at the middle of 

 the body. 



^ These organs, until now regarded as ovaries, 

 secrete only vitelline cells. With most Trematodes 

 their nuclei are clear, and have been taken for 

 eggs. In eggs recently formed, one can always 

 distinguish these cells from the germs. In passing 

 the excretory canals they are compressed and 

 elongated, but never run into each other. When 

 these canals are crowded, they have the aspect of 

 white cords, which have often been t;iken for 

 nerves. But when they are empty, they, as well 

 as the vitellus-secretuig organs, are almost invis- 

 ible.! 



* [§ 115, note 1.] See upon this subject Van 

 Beneden (Ann. d. Sc. Nat. XI. 1849, p. 326), who 

 has described in detail the sexual organs of Lin- 

 guatula Diesingii, and has shown the se.xes to be 

 separate. See also my note under § 99. — Ed. 



t [ § 115, note 7.] To say that certain organs 

 8ecrete vitelline cells, is a little obscure, and no 

 doubt Siebold intended to convey the meaning 

 that they secreted the plastic material out of which 

 these cells are formed. I make this perhaps 

 seemingly unnecessary reference to the matter, 

 since it concerns the subject of the development of 

 the ovum. In the Ascari.i, where tlie origin and 

 development of the ovum can be satisfactorily 



studied, you first notice the germs as nucleolated 

 cells, of which the nucleus is the future germina- 

 tive vesicle and the nucleolus the germinative dot. 

 These cells increase in size, and as they move 

 along there appear in the liquid which lies between 

 the nucleus and the cell-wall minute granules 

 which ultimately become cells ; in this way the 

 vitellus is formed, the formation being endogenous 

 and not exogenous. These special organs or 

 tubes therefore are vitellus-forming organs, in vir- 

 tue of their secreting the formative material out 

 of which the vitellus is formed within the original, 

 nucleolated germ-cell. — Ed. 



