22 BUSK, ON THE STRUCTURE AND 



outer portion of each ovary is a dense granular tract (fig. 6, a), 

 the remainder of the cavity being occupied by a more finely 

 granular stroma in wrhich the ova are developed, attached at 

 first by short pedicles to the placental tract. Tn the outer 

 portion of this tract runs a slender csecal canal, which may be 

 traced close to the opening of the oviduct (fig. 6, b). This 

 canal, which was first noticed by Wilms (1. c. p. 13, fig. 10), is 

 regarded by Krohn (Wiegm. Archiv. 1853, p. 269), as a 

 receptaculiim seminis, seeing that it is occasionally found to be 

 filled with actively-moving spermatozoa. According to Wilms 

 and Huxley, the canal is lined with cilia, but Krohn is of 

 opinion that this appearance of cilia is due to the presence of 

 the motile spermatozoids. The ova (fig. 6, c) present no 

 peculiarity, except that Wilms and Krohn concur in stating 

 that a germinal spot is never observed in the comparatively 

 large germinal vesicle. 



2. The male apparatus. — The caudal portion of the animal 

 (fig. 1, d) is divided by a vertical, longitudinal septum, into 

 two perfectly distinct compartments. These compartments 

 may properly be termed the testes, as it is them that the deve- 

 lopment of the spermatozoa appears to take place, which is 

 thus described by Wilms (1. c. p. 13). In younger individuals, 

 each compartment contains a greater or less number of vesicles 

 of various dimensions, some spherical, others of irregular form, 

 elongated, and ovoid. At first sight they seem to be filled 

 with a sort of granular substance, but when a little larger, are 

 plainly seen to contain minute spherical cells. In animals 

 nearer maturity, besides these cysts, there will also be noticed 

 cells in which, upon the addition of acetic acid, a nucleus is 

 plainly visible. From these aggregations of cells (fig. 9), 

 which are always somewhat less in size than the cysts above 

 noticed, the spermatozoa are developed. At a certain period, 

 slender filaments are seen to proceed from them, causing the 

 appearance as if the cells were beset with spines, whilst others 

 present the appearances represented in fig. 12, a, b, indicating 

 a further stage of development. The central cellular mass 

 (shown at a, fig. 12) gradually diminishes in bulk as the 

 filamentary portions become more and more developed (fig. 12 

 5), and gradually disappears altogether, nothing remaining but 

 bundles of spermatozoids attached to each by their heads. 

 These bundles eventually break up into separate spermatozoids. 

 The mature spermatozoid is a long filament, slightly enlarged 

 at one extremity, beyond which, however, the point is usually 

 prolonged in the form of a very delicate short thread (fig. 11). 



A remarkable ciixumstance observable in the sj)ermatic 

 cavities of Sagitta, is the continual cyclosis performed by their 



