§129. 



THE TURBELLARIA. 



139 



The following are the parts usually found : an ovary or organ of vitel- 

 line secretion, which is double, and, extending into the parenchyma of the 

 body, opens by a common excretory duct into a large cavity, — a vagina or 

 oviduct ; a double testicle sends its seminal liquid, full of filamentoid and 

 motionless spermatic particles, into the seminal vesicle through two tor- 

 tuous vasa deferentia; to this seminal vesicle is attached a very erectile 

 penis, situated by the side of the vagina. There is a common genital open- 

 ing, situated always behind the mouth, for the protrusion of this penis and 

 the escape of the eggs. 



With Planaria, there are, beside, two special, hollow organs, with narrow 

 excretory ducts, which open into the vagina. Of these, one very probably 

 secretes the envelope of the egg, while the other serves as a Receptaculuvi 



§ 129. 



The embryonic development of the Turbellaria is yet unknown except 

 with the Planariae. 



It differs wholly from anything yet known with other Invertebrates. 

 Many of these embryos are developed, always simultaneously, in one 

 large egg; but it is impossible at first to determine their number, since 



4 See, for the genital organs of Me.sostoinum Eh- 

 renbergii, Focke (loc. cit.); for those of Pte?io- 

 cera, and Leptoplana, Mertens (toe. cit.); and for 

 those of Lferostomum, and P/anaria, Duges, 

 Baer, and Orsted (loc. cit.). But the interpretation 

 here given of the different parts of these organs 

 must be much changed. For, to speak here only 

 of the genus Planaria, what Baer has regarded 

 as the ovaries and oviducts, are certainly the two 

 testicles with their vasa deferentia, since I have 

 always found them filled with spermatic particles 

 (loc. cit. Tab. XXIII. fig. IS, a. b.). The two sem- 

 inal canals open into a hollow, flask-shaped body 

 like a Vesicula seminalis or a Ductus ejacu- 

 latorius, the neck of which is continuous with a 

 very contractile and erectile tube (Penis). This 

 penis is in a cavity separated by a septum from 

 the large vulva, with which, however, it communi- 

 cates by a special orifice, and consequently can be 

 protracted through the common genital opening. 

 There is, beside the intestinal canal, another rami- 

 fied organ in the body of Planaria, and which 

 very probably is an ovary, or at least a vitellus- 

 secreting organ. But its caeca contain only simple 

 vesicular bodies, which have no germinative vesi- 

 cles. The canal which Dugis (loc. cit. XV. PI. V. 

 fig. 4, b.) has taken for an oviduct, belongs prob- 

 ably to the ramifications of this organ. The other 

 two organs which this author (Ibid. PI. V. fig. 4, 

 8, c.) has described as Visicule copulatrice ou 

 reservoir du sperme et des oeufs, do not appear 

 to me to exist in all Planariae. They consist of two 

 hollow, pyriform organs, not blended together as 

 Dugis has figured them, but distinct ; one opens 

 by a long, and the other by a shorter canal, into 



* [ § 12S, note 4.] See, for many details on the 

 sexual organs of the TuEj)ellaria, and illustrated 

 with figures, Schmidt, loc. cit. (Protostomum, 

 Fortex, Hypostomum, Derostomum, Meso- 

 stomum, Opistomum, Macrostomu7n, Microsto- 

 mum, Stenostomum, Schizostomuni, Tijphlo- 

 plana; according to this author, Dinopkilus vor- 

 ticoides is separate-sexed, — the exceptional in- 

 stance among the Rhabdocoeli. The subject of the 



the vulva. As I have found many spermatic par- 

 ticles in the first of these, I am led to regard it as 

 a Receptaculum seminis. But in the other, 

 which Baer (loc. cit. Tab. XXXIII. fig. 18, e.) has 

 taken for a penis, I have never found either eggs 

 or germs, but always only a granular substance ; 

 from tills I am inclined to think that this organ se- 

 cretes the material which envelops the vitelline 

 cells grouped in the vulva. With the Planariae, 

 one egg at a time is always formed in the round 

 vagina ; this is very large, and when it is de- 

 posited others succeed it in the same way. This is 

 not true, however, with Mesostomum Ehren- 

 bergii ; here the vagina is short and narrow, 

 and receives various organs whose nature is 

 not yet well determined. One of these contains, 

 accorduig to my own researches, a confused mass 

 of active, filamentoid spermatic particles, and may 

 therefore be regarded as a Receptaculum sem- 

 inis. Two canals which pass off right and left 

 from the vagina, bifurcate into two simple coeca, 

 one of which passes forwards, and tlie other back- 

 wards, and in which very large eggs remain for a 

 long time. This therefore may be regarded as an 

 uterus. See Focke, Taf. XVII. fig. 1, 11, g. g. 



According to the very minute researches of 

 quatrefases (loc. cit. p. 163, PI. IV.-VIII.) made 

 upon various marine Planariae, both the male and 

 the female organs of these DendrccoSli have two 

 distinct orifices situated in the ventral region, one 

 behind the other. The posterior is a vulva and 

 opens into a more or less long coecum (vagina or 

 copulatory pouch) upon which are laterally inserted 

 two oviducts. The anterior orifice is for the pro- 

 trusion of the protractile penis.* 



spermatic particles of the Planariae is littleunder- 

 stood. They probably have not a hair-like form as 

 mentioned in the preceding note, but are Cercaria- 

 like ; see Kolliker, loc. cit., (^uatrefages, loc. cit. 

 PI. VIII. fig. 5-9, and Schmidt, Die Rhabdoc. 

 Strudelwurmer, &c., p. 16 ; this author, however, 

 describes those of Opistomum, pallidum as some- 

 what different, there being a filament beyond the 

 head (Taf. V. fig. Ut.). — Ed. 



