034 R. J. HARVEY GIBSON ON THE 



to be composed of a central stalk, evidently formed by the union of the several 

 filaments of a number of heads, which are arranged around the stalk in an 

 extremely graceful manner. Very careful focussing, under a power of 800 

 diameters (after long staining), is necessary before the separate filaments can 

 be seen (PI. CLIII. fig. 79). 



Isolated sperms show themselves to be composed, as in the case of mam- 

 malian and other sperms, of a head and tail. The head is oblong, about & 2oc> 

 of an inch in length, and about a third of that in breadth, and apparently 

 structureless. It takes on a deep stain with picro-carmine. The tail is very 

 slender, being not more than ^.thnr of an inch in breadth by about 1( / 00 of an 

 inch long. It takes on scarcely any stain after an hour's immersion in picro- 

 carmine ; the head, meanwhile, as already stated, becoming deeply stained of a 

 crimson colour (PI. CLIII. fig. 80). 



Female. — In principle, the structure of the female generative organ is some- 

 what similar to that of the male. Like the male organ, it is more or less 

 wedge-shaped, and usually larger in size. It is covered by a very delicate 

 membrane composed of connective tissue, and covered with squames, of which 

 latter the nuclei are the most evident parts. The gland itself is merely a bag, 

 with a fibrous wall puckered externally and covered by a cubical epithelium 

 many layers deep ; the superficial layers of which become free, and fill the 

 cavity of the gland as ova. The ova are of all sizes, from that of the cubical 

 epithelial cells to spheres which can be perfectly easily seen with the naked 

 eye. The cubical epithelium is more abundant in certain spots, which, as in 

 the case of the testis, may be termed " nests." 



An ovum (PI. CLIII. fig. 70) fully developed is polygonal, or, when free, 

 rounded mass, about from y^y to ^ of an inch in diameter. It is covered 

 externally by a stout capsule, structureless, or vertically striated and punctured. 

 The protoplasm is made very opaque by the presence of a very large quantity 

 of yolk spherules. A nucleus containing nucleolus and endo-nucleoli is always 

 visible after staining or crushing. In the younger ova, however, it is easily seen. 



Historically, with the exception of Fischer's researches on development, 

 very little indeed has been done towards the elucidation of the structure of the 

 reproductive organs. In fact, any observations made on the system have been 

 mainly as to whether ducts are present or not, and if so, whether or not the 

 "capito-pedal orifices " are the openings of these ducts. Cuvier (Joe. cit.) de- 

 scribes and figures an oviduct, which no one since his time has been able to find. 

 Dall thinks he has seen a duct " from the extreme left of the gland, and open- 

 ing into the dendritic renal sac" (Amer. Jour, of Conch., 1871, vi. 271). In 

 another later paper, however (Proc. Acad. Philacl., 1870, 239), he denies all 

 knowledge of an oviduct ; he denies the very existence of Lankester's " capito- 

 pcdal orifices " in the first-quoted paper, but admits in the second that they are 



