MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 177 



to believe that the pyriform sac was a vestige of an organ which, at some former period in the 

 history of the species, had formed a communication between the venous sinus and systemic 

 ventricle, independent of the branchial circulation. 



Kefkkstkin discovered the opening of the sac to the exterior. 



Many years after Lankester and Bourne firs! discovered the presence of the organ in the 

 male Nautilus, and showed that it has the .same structure and position in both sexes. These 

 authors called attention to the exactly similar position of the genital duct upon the right side of 

 the body and the pyriform sac and its duct upon the left side, and suggested that the latter is the 

 left genital duct in a vestigial condition. The similarity of the functional and non-functional 

 genital ducts is evident in the female, in which the aperture of the oviduct occupies a position 

 upon the right side of the body corresponding closely to the position of the aperture of the 

 pyriform sac upon the left side. 



Later observers have added still further evidence in favor of the homology of the pyriform 

 sac with the functional genital duct. Kerb finds that in a very young female the inner part of 

 the genital duct has exactly the appearance of the pyriform sac in the adult, the rudiment of the 

 gonad being quite distinct and apparently median and unpaired. 



The first part of the statement adds great strength to the view which considers the pyriform 

 sac to be a left genital duct. The latter part of the statement answers the question left open by 

 Lankester and Bourne — whether the pyriform sac represented only the left genital duct, or the 

 genital duct and the gonad of the same side. 



Kerr also remarks that "in the young animal, the Needha.m"s sac (spermatophore sac) being 

 not vet expanded, the form and size of the right portion of the apparatus (penis) are in almost 

 exactly the same condition as is the left in the adult." 



The discovery by Willey of the symmetrical arrangement of the arteries of the gonad and 

 genital duct and the pyriform sac entirely justifies the conclusion that the latter two are 

 homologues. The fact that from both the gonaducal artery and the artery of the pyriform sac 

 a branch is sent to the ovarial membrane forms a strong piece of evidence that these are equiv- 

 alent arteries, and also indicates that the pyriform sac corresponds to the genital duct alone, and 

 not to an entire left reproductive apparatus. 



It is then about as well established as anatomical evidence alone, can establish such facts, 

 that Nautilus possesses a single unpaired, median gonad, and a pair of gonaducts; one of these, 

 the right, is functional and highly developed; the other, the left, exists in the condition of a 

 sac opening to the exterior, and no longer functions as a gonaduct. 



The spermatophore is formed in the vas deferens. Apparently the formation takes place in 

 the thickened portion of the vas deferens, as in the specimens I have dissected the spermatophore 

 ended at about the commencement of this portion of the tube — either a little distal or proximal 

 to this point, As the spermatophore is formed it, is moved forward and finally it debouches in the 

 seminal vesicle, where it is irregularly and loosely coiled. From here it passes into the spermato- 

 phore sac where I have always found the coil occupying the two sacs, bent around the longitudinal 

 septum in the form of a U. I have next found the spermatophore occupying the tip of the penis, 

 causing a great distention of this organ. The spermatophore is now tightly coiled into an ovoid 

 mass, about 8 millimeters in length by 5 millimeters in diameter. 



From the penis the spermataphore is in some way passed to the superior labial tentacles. I 

 have several times found a single spermatophore tightly held by the upper tentacles of either the 

 right or left superior labial group. But when among the labial tentacles the spermatophore is 

 always surrounded by a closed, tough sac of a chitinous material. The sac with the spermato- 

 phore inside it forms a roughly spherical mass, averaging 13 millimeters in diameter. The 

 spermatophore is loosely coiled and lies free inside the sac. 



We find here two questions to be answered. The first is, How and where is the sac formed 

 around spermatophore 3 One would naturally expect such a structure to be formed either in the 

 spermatophore sac or the penis. But I have never found a sac around a spermatophore contained 

 in the spermatophore sac or in the penis — only around those held among the labial tentacles; but 

 around each of these. Possibly the secretion of Van der Hoeven's organ forms the sac 



