142 B. W. MACBETDE. 



Genital Organs. 



The formation of the genital organs need not detain us long, 

 as it is very simple. Amphiura squamata is hermaphrodite, 

 and the general disposition of the genitalia has been described 

 when speaking of the adult ovoid gland. 



The ovaries appear first as small swellings of the genital 

 rachis (compare figs. 16 a and b). The rachis here lies in the 

 sinus in such a way that it touches the wall of the bursa from 

 the first. The latter is here very thin, and one can detect a 

 small involution towards the ovary. Here of course, when 

 fully developed, is the point of discharge of the organ. The 

 further history of the ovary merely consists in the increase of 

 the number of the primitive germ-cells and of the subsidiary 

 cells. Finally, one or two primitive germ-cells get the upper 

 hand and form the fully developed ova. Of these there is 

 usually only one in an adult ovary ; when it is discharged one 

 of the undeveloped primitive germ-cells takes its place. 



Fig. 17 shows the passage of the young ovary into the 

 rachis, and fig. 18 shows the ovary of a small adult. 



When the ovary commences to form, the branch of the 

 rachis leading round the bursa into the radial testicular 

 chamber is undeveloped. Its formation is shown in fig. 12. 



The first stage in the development of the testis (fig. 13) is 

 indistinguishable from that of the ovary, viz. a solid mass of 

 cells, except that these appear to consist more exclusively of 

 Urkeimzellen. Afterwards a lumen forms as the rudiment 

 increases in size (fig. 14), as sometimes occurs in old ovaries 

 when more than one egg comes to maturity at a time. The 

 Urkeimzellen are finally confined to one or two peripheral 

 layers, and the centre is occupied by the products of their 

 division. In neither the ovary nor testis did I see the least 

 trace of a matrix of plasma and fibres, such as Cu«^not (4) has 

 described. Into the maturation of the sexual products it is 

 not my purpose to enter. I only call attention to the follow- 

 ing fact. Cuenot (4) states that in the testis the central 

 Urkeimzellen are destroyed. I have seen no trace of this; 



