STUDIES OX THE E< 'TOPARASTTIO TREMATODES OF JAPAX. J 35 



Sfenital .'ttriniu sliould h^ ivLi'irdecl as the invaofiiKition of a portion of 

 the surface of the Ixxly. We Imve as yet no adequate embryological 

 proofs on this point ; hut tlie f;ict that tlie investing membrane of 

 the body is in many cases directly continued, at least for a certain 

 distance, into llie atrium, and the m:ujy gradations in form of 

 this cliamber from tlint of a mere ])it to tliat of a deep and spacious 

 cavity seem t<^ me to Jend very strong support to tliis view — a view 

 wliich lias recently found expression from another side"-* 



The genital atrium is most developed and presents the most 

 varied forms in MicrocotijJc. In this genus it is a deep cave-like cavitv, 

 into which the y;is deferens and the uterus open, and communicates 

 with the exterior by means of a minute opening, the ponts gcuitalis com- 

 munis. Its inner surfice is lined by a thin but dee])ly staining mem- 

 Ijrane which in sections is seen to be fjrmed l)y the direct continuation 

 and gradual thinning of the investing membrane of the body (Pis. \, 

 &j VI), and is covered in all the species with hollow, chitinous spines. 

 In M. dayins (PL \, fig. 2.) it is a somewhat reniform cavity, with 

 the part correspt^nding to the hilus directed oblicpiely forwards and 

 towards the ventral side, into which the uterus opens close to the ex- 

 ternal pore, while the vas deferens opens more on the dorsal side almost 

 opposite the hilus. The conical spines which are mainly confined to 



1). The results obtained by Voeltzkow in Ai^pidogaater condticola (Würzburger Arbei- 

 ten, Bd. 8, 183S, p. 279) do not seem to me to decide the question. According to this naturalist 

 the " Penisschlauch" and the "Vulva" arise "als solider, von der Haut am Anfang des 



Halses, schief nach hinten und oten aufsteigender Zapfen an." Referring to the figure it 



seems to me that tha solid mass of cells which becomes afterwards the " Penisschlauch " and 

 the " Vulva "■' is not of an ectodermal origin but mesodermal ; for the true ectoderm is already 

 in this stage transformed into a membrane. If I may put my own interpretation on the figure 

 of another, the solid mass of cells aljove referred to is prol^ably differentiated into the peculiar 

 connective tissue that constitutes the penis ; and in this case the lining of the " Penissehlanch" 

 would alone be derived from the ectoderm. 



2). Montlcelli — Primo contributo di osservazioni sui Distomidi (Studii sui Trematodi endo- 

 par.issiti), p. 86. Spengel's Zool. Jahrbücher, III. SuppL, 1893. 



