322 THE CEPHALOPODA 



neighbourhood. This follicle is nourished by an important vascular 



supply, and its surface of contact with the ovum is increased by the 



formation of equatorial and meridional folds (Fig. 285, fo) which 



penetrate into the substance of the ovum and secrete the vitellus. 



This vitellus forms an increasingly large part of the mass of the 



ovum and pushes the formative protoplasm and 



the nucleus up to its narrower pole opposite to 



|||l| the peduncle of attachment. 



When mature the ovum acquires a chorion 

 t ; ; : il with a micropyle, escapes by dehiscence of its 



H external envelope into the coelomic cavity or 

 f genital capsule (Figs. 252, coe; 278, g.c), and 

 passes into the genital duct. In its passage 

 through the oviduct the egg traverses a more 

 or less voluminous glandular enlargement of the 

 egg^Tsp'ir^^/ol'ovuiar duct > situated on the wall of the genital capsule 

 follicle ; vi, vitellus. itself i n Nautilus, at the middle of the duct in 



(Alter Huxley and Pel- . 



seneer.) the Octopoda, near the free extremity of the duct 



in the Decapoda. This glandular enlargement is 

 formed of two distinct portions in the Octopoda (Fig. 278, o.g) and is 

 feebly developed in Argonauta, Avhose eggs are protected by the 

 external shell. In addition to the true oviducal glands there are 

 other accessory glands, unrelated to the genital ducts, in female 

 Cephalopods. These are differentiations of the wall of the pallial 

 cavity, and occur on the pallial wall in Nautilus (Fig. 270, n), but 

 on the somatic wall in the Dibranchia. In the latter order they 

 form two distinct masses, one on either side of the rectum, Avhereas 

 in Nautilus they form a continuous mass (Fig. 276, g.n}. In certain 

 Oigopsida (Enoploteuthis, Cranchia, Leachia) and in the Octopoda 

 these organs are absent. In the Dibranchia these " nidamentary " 

 glands open near the genital orifice, and are generally accompanied 

 by a second pair, as, for example, in Sepia : they produce the 

 external envelopes of the eggs, formed by an elastic substance which 

 hardens rapidly on contact with the water. 



In the male, the testis is the specialised portion of the coelomic 

 wall from which the spermatozoa are developed (Fig. 286, III) : its 

 structure is comparable with that of the ovary. The spermatozoa, 

 when mature, pass through an orifice into the genital capsule 

 properly so called, and thence into the spermiduct which originates 

 from the wall of this capsule and opens externally into the pallial 

 cavity, on the right side in Nautilus (Fig. 275, pe), on the left side 

 in the Dibranchia (Fig. 286, VIII). Certain glandular pouches and 

 a terminal reservoir are found on the course of the spermiduct. 

 Nautilus has only one glandular pouch, but in the Dibranchia 

 there are, as a result of specialisation, two pouches: (1) the 

 vesicula seminalis, which is a simple enlargement; (2) the prostate. 



