MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 179 



How is the protective envelope of the spermatophore destroyed? There is no evidence as 

 yet to indicate whether this is done by the male, or if the envelope is intact when the female 

 receives the spermatophore. In the latter ease the envelope may be destroyed l>y the action of 

 the secretion of the receiving lamellae, or more actively, by the tentacles after i icing received, 

 or by the handling it may undergo during the transfer from the male to the female. 



I do not know of anyone who has ever found spermatophores upon any other region of the 

 hotly of the female Nautilus than the one described. 



Another question arises. How long i> the spermatophore, retained among the tentacles of 

 the male or upon the receiving apparatus of the female? lam inclined to think that the sper- 

 matophore may be retained for a variable but not usually long time among the tentacles of 

 the male. I have several times found a spermatophore in the process of formation within 

 the vas deferens, and another coiled up in the spermatophore sac. In another case the 

 spermatophore sac contained one spermatophore while another occupied the tip of the penis. 

 The comparatively immense size of the fully developed testis indicates that it can produce an 

 enormous number of spermatozoa in a very short time. The accessory eland, too, is of a size 

 which shows that it can very quickly produce the secretion required for the tubular walls of a 

 spermatophore. Spermatophore after spermatophore is probably produced in rapid succession 

 throughout the breeding season; or if this is continuous, the year round, as Willey suggests, 

 throughout the period of sexual activity. It seems probable that the males carry a spermatophore 

 among the tentacles only till it can be transferred to a female. Then another spermatophore takes 

 the place of the first, and so on. The female may carry the spermatophore for a longer time. 

 Apparently a single one is carried at any time. 



THE CIRCULATION. 

 ARTERIAL CIRCULATION. 



The figures of the arterial circulation have been made partly from my own dissections and 

 partly from the published figures and descriptions of Willey. In some instances I had obtained 

 the same results as Willey before he published his figures, in others I have merely verified his 

 work, and in places I rely entirely upon his figures and descriptions in order that my own 

 descriptions may be as complete as possible. Some facts are, I think, published for the first 

 time. 



In the case of the branches of the lesser aorta and the arteries of the reproductive apparatus 

 the completeness of the account is entirely due to the researches of Willey. 



In both figures of the arterial system the arteries are viewed from the dorsal side. As the 

 vessels represented in text-tig. 11 lie almost entirely ventral to those of text-fig. 10, 1 believe 

 that they are shown with less danger of confusion in separate figures. 



The heart is situated immediately back of the mantle fold in the portion of the coelom known 

 as the pericardium. It is an oblong muscular organ of quite considerable size, being '2 centi- 

 meters in width, 1 centimeter in length (antero-posterior measurement), and 6 to 8 millimeters 

 in thickness. The long axis of the heart is exactly transverse to the long axis of the body. The 

 right side of the heart is slightly longer than the left side, so the symmetry of the heart is not 

 quite perfect. 



A branchial vein enters each corner of the heart. The portion of each branchial vein near 

 the heart is capable of considerable distension, and these portions have been called the auricles 

 of the heart. But very frequently one or all these vessels show no increase in diameter near the 

 heart. This fact indicates that the so-called auricles of Nautilus, while physiologically similar, 

 have not the same morphological importance and should not be considered as organs of the same 

 nature as the auricles of the heart of the Gastropoda and the Lamellibranchiata. In these classes 

 the auricle forms a distinct chamber, which even in its development is distinct from both the 

 ventricle and the branchial veins, which the auricles of Nautilus are not. The term is a con- 

 venient one anatomically, indicating the portion of the branchial vein inside the pericardium 

 Vol. 8— No. 5 6 



