DORIS. 



There are two spermathecse and two channels ; one of these latter leads from the 

 exterior to the spermathecse, the other from them to the oviduct. The orifice of the vagina 

 or external channel lies above and between the male and ovarian outlets. The vagina (n) 

 is large, longitudinally plicated internally, and opens freely into the principal spermatheca (/£)• 

 This is a large, globular sac of a purple-brown colour, lying between the male and female 

 parts. Just where the vagina opens into it, the channel (/) leading to the oviduct leaves it. 

 This channel is soon joined by the minute duct from the accessory spermatheca (m), and then 

 unites with the oviduct, where it sinks into the mucus-gland. 



The reproductive organs are thus arranged in JD. tuberculata ; and, notwithstanding- 

 numerous modifications in the various species, the connexions of the parts are the same in all. 

 In JD. bilamellata, D. pilosa, D. repanda, and D. aspera, the testis diminishes in length, and 

 increases in thickness. In JD. repanda it has appended to it a constricted duct-like tube, that 

 keeps up its connexion with the intromittent organ. In D. Johnstoni and JD. coccinea the 

 testis (fig. 8 c) is composed of a large, glandular, fusiform mass, bent upon itself, and made 

 up of a minutely convoluted tube. One end of this mass is connected to the intromittent 

 organ (a) by a short duct {b), and the other communicates with the oviduct (/) at the usual 

 place of its union with the testis. 



In addition to this interesting modification of the testis, D. Johnstoni is furnished with a 

 solid stiletto, contained within a sac (fig. 8 o, and fig. 10 a, b) placed in front of the penis; 

 this stiletto (figs. 9, 10, 11) is capable of being protruded through an orifice (fig. 9/) proper 

 to itself, situated at the extremity of a long penis-like organ (d), and the bottom of the sac 

 receives one end of a slender duct, which comes from a large glandular body (fig. 8^). The 

 stiletto is probably an instrument of excitement, like the dart of the common snail. 

 Spermatozoa (fig. 12) are found in vast abundance in the spermathecse, and in the dilated 

 portion of the oviduct. In the principal spermatheca they are mostly in a state of develop- 

 ment, contained in large fusiform spermatophora ; in the accessory spermatheca, they are 

 always mature and arranged in parallel order, but in the dilated portion of the oviduct they 

 are confusedly crowded together. The head of the spermatozoa is slightly enlarged, fusiform, 

 and bent considerably to one side ; the tail being very delicate, long, linear, and generally 

 undulated. 



The heart lies upon the upper surface of the posterior part of the liver-mass, immediately 

 below the skin, and just in front of the branchial circle. It consists of an auricle (PI. 1, fig. 2 k) 

 and a ventricle (j) enclosed within a membranous pericardium (i). In addition to these parts, 

 there is another propelling organ (n) lying under the pericardium, and opening into it. The 

 great systemic artery (PI. 2, fig. 1 o) comes from the front or apex of the pyriform muscular 

 ventricle, and gives off branches to the various organs. The blood so distributed, with the 

 exception of that sent to the liver-mass {/), becomes extravasated among the tissues, and 

 thus finds its way into the general visceral cavity, and thence by orifices in its walls into the 

 regular network of sinuses or spongy tissue of the skin. It then passes into a great lateral 

 trunk-sinus running backwards on each side of the body, and reaches the lateral angles of 

 the auricle by distinct systemic veins (PL 1, fig. 21,1). This portion of the blood never 

 reaches the gills ; it is only that which goes to supply the liver-mass that passes through the 

 specialised breathing organ. The blood supplied to this mass, which comprises liver, ovary, 

 and renal organ, passes into minute venous branches, which converge and unite into a 



