570 H. p. KJERSCHOW AGERSBORG 



of the penis. The structure of the seminal vesicle and of the 

 ampulla is alike ; it consists of a heterogeneously arranged 

 cell-mass, so well welded together that the whole structure is 

 quite compact. The penis is, indeed, so large that when it is 

 withdrawn it fills a large part of the body-cavity. The penis 

 is simply an extension of the seminal vesicle. The sheath 

 of its anterior portion is firmly lodged on the mucous gland 

 (PI. 37, fig. 81, Cl.p) with the penis in its pore. The penal pore 

 merges with the body-wall, adjacent to the vaginal orifice 

 (PL 37, fig. 77, Mga, Fv). The penis is sometimes extended 

 to the outside, and is then curved like a screw (PI. 27, fig. 8, P). 

 In copulation the penis, which is long, twisted like a screw 

 and of tough musculature, is inserted into the posterior (female) 

 genital pore of the mate, and so firm is the union that separation 

 may not occur even though the couple be dipped from their 

 natural abode and placed in a vessel (Agersborg, 1921 : 238). 

 I have not found mutual coitus effected at the same time 

 in this species, although it is supposed to be a common practice 

 among nudibranchs, according to difi'erent authors : Alder 

 and Hancock (1845: 25), Mazzarelli (1891a: 237), Crozier 

 (1919) et al. 



(6) The Mucous Gland. 



The mucous gland constitutes the albuminous and nidamental 

 glands (PL 37, figs. 74, 76, 79, Mg, 81, Mgl, and 84, A, B, C, D). 

 It consists of laminations so arranged that sections through 

 the side of it have a six-layered aspect ; continuous sections 

 soon bring out the true conditions. The gland is made up of 

 simple, tall, ciliated columnar epithelium, highly glandular in 

 nature, and which rests on thin connective -tissue fibres with 

 cells which connect the gland to the body-wall. The gland 

 extends almost to the outside of the vaginal orifice (PL 37, 

 figs. 74, 76, 77). It functions when the animal spawns ; the 

 mucus and the capsulated eggs pass out together. 



Mazzarelli (1891), in P 1 e u r o b r a n c h a e a , finds that the 

 vagina at the back of the oviduct's terminal point prolongs 

 itself remarkably dorsad becoming sacculated, its walls being 



