174 



THE ANATOMY OF IXVERTEBRATED AXIMALS. 



ed masses lying in the sucker. At first sight it appears to be 

 oval, but it is, in fact, pyrif orm, the larger end being anterior, 

 while the posterior narrower extremity is bent backward be- 



Fig. 41.— A, water-vascular system of Aspidogaster conchicola : a, terminal pore ; 

 b, lateral contractile vessels ; c, lateral ciliated trunks, that of the left side shaded ; 

 d, dilatation of this trunk ; B, one of larger, and C, one of the smaller, ciliated 



vessels. 



neath the anterior end. Before it reaches the anterior ex- 

 tremity of the mass, however, it is bent sharply back again, 

 parallel with itself, and so passes into the oviduct (Fig. 40, i). 

 The ovary is surrounded by a delicate, but strong coat, inclos- 

 ing a mass of transparent protoplasm. At the anterior end 

 of the ovary minute granules are scattered through this sub- 

 stance, and are occasionally surrounded by a faint, clear area 

 (Fig. 43, A 1). These are the rudimentary germinal spots 

 and vesicles of the future ova, the course of whose develop- 

 ment may be readily traced by working from the anterior to 

 the posterior extremity of the ovary. The germinal spots 

 beeome larger, and gradually assume the appearance of vesic- 

 ular nuclei ; while the clear area around them in like manner 

 becomes larger, and acquires more and more the appearance 

 of a cavity. While this cavity is small, it has no distinct 

 wall, but, as it enlarges, the contour of the wall becomes dis- 

 tinctly marked (Fig. 43, A 2, 3, 4). On examining the ovary 

 close to the commencement of the oviduct, a division of the 

 homogeneous protoplasmic basis or matrix of the ovary into 

 areas surrounding each germinal vesicle becomes obvious. On 

 the application of pressure, the matrix breaks up into masses 

 corresponding with these areas in size, which are very flexible, 

 but when left to themselves assume a rounded or oval form, 

 and have all the appearance of perfect ova, except that they 

 possess no vitelline membrane, and that the yelk, instead of 

 being granular, is clear, and comparatively small. These 



