This section is from the book "General Outline Of The Organization Of The Animal Kingdom, And Manual Of Comparative Anatomy", by Thomas Rymer Jones. Also available from Amazon: A General Outline of the Animal Kingdom and Manual of Comparative Anatomy.
This sacculus is, in fact, filled with innumerable white filaments, each about half an inch in length, arranged parallel to each other, and disposed with much regularity. There are three or four rows of them, one above another, entirely filling the sac; and they are maintained in situ by a delicate spiral membrane, but are quite unconnected with the sac itself. The filaments when taken out, even long after the death of the Cephalopod, exhibit, when moistened, various contortions, and by some have been regarded as Entozoa.
Fig. 298. Generative organs of the male Cuttle-fish. (After Cuvier).
(1606). These remarkable spermatic filaments (the famous "filament machines" of Needham) present, in fact, a very complicated structure. Their form varies in different species; but in their essential composition they are all found to consist of a long tubular sheath (fig. 297, 2,3), composed of two membranes, and enclosing a long tube, convoluted upon itself like an intestine, which is filled with an opake white fluid, in which are contained millions of zoosperms; and the apparatus to which it is attached anteriorly constitutes an ejaculatory instrument, by the aid of which the spermatic secretion is forcibly ejected. These "spermato-phores" as they have been named by Milne-Edwards, serve as vehicles for the conveyance of the seminal fluid into the generative system of the other sex, notwithstanding the absence of any copulatory apparatus.
(1607). A most extraordinary modification of the male sexual organs is met with in the males of the Argonaut, Tremoctopus, and probably of other kindred genera, in which one of the arms is so strangely modified, both in its shape and structure, that Cuvier mistook it for a parasite, describing it, under the name of Hectocotyles, as "a long, parenchymatous worm, compressed at the anterior extremity, where the mouth is situated, having its inferior surface furnished with suckers, from sixty to a hundred in number, arranged in pairs, and furnished with a sacculus, situated at the posterior extremity of its body, which is filled with the folds of the oviduct".
(1608). The Hectocotylus Argonautce*, as this strange appendage is still called, is,in fact, a portion of the Argonaut itself, developed in a remarkable sac, which supplies the place of the left arm of the third pair. The male Argonaut (fig. 299,1, 2) is of very small size as compared with the female, being not more than an inch in length, and has no shell; moreover the upper pair of arms are not, as in the female (fig. 283), expanded into velae, but are pointed. The sac above alluded to, on being opened, is invariably found to contain a solitary Hectocotylus, the dilated portion of which is attached at its base, whilst the rest of this remarkable organ is free and rolled up towards that side upon which the suckers are situated; but as soon as the sac is opened, or when it is ruptured by the movements of the contained Hectocotylus, the latter unfolds itself (fig. 301, a), assuming so exactly the appearance of a parasitic animal that the mistake committed by Cuvier is by no means surprising. The Argonaut itself possesses a well-developed testis, according in its structure with that of ordinary Cuttle-fishes, and which contains spermatozoids in different stages of development; but its excretory duct terminates in the Hectocotylus, which is evidently nothing more than one of the arms of the Argonaut thus strangely developed. But, what is stranger still, this arm, arrived at maturity, detaches itself from the Argonaut, and from that moment enjoys an independent existence. It lives adherent to a female Argonaut, which it impregnates by a real coitus; so that in this respect, as well as by its movements, and by the length of its life after its detachment, it might be mistaken for a complete male animal. Still it cannot be regarded as an independent being, seeing that it has no alimentary apparatus; neither is it the organ whereby the seminal fluid is produced, but simply a vehicle whereby the male secretion is transported.
Well indeed does it deserve the epithet bestowed upon it by Cuvier, who, ignorant of its real nature, pronounced it "un ver bien extraordinaire!" (1609.) From the pouch of Needham a short canal leads to the penis (h), a short, hollow, muscular tube, through which the fecundating fluid is expelled.
Fig. 299. 1, 2. Male Argonaut, of the natural size, represented in front and in profile, showing the sacculus in which the Hectocotylus is contained; from a specimen preserved in spirit. 3. Sacculus, in which the Hectocotylus may be distinguished through its transparent walls. The specimen from which this figure was taken having been preserved in spirit, is, of course, contracted in all its dimensions.
* Henri Muller, Ann. des Sc. Nat, 1851.
Fig. 300. 1. Sacculus of Argonaut laid open, showing the abnormal arm (Hectocotylus) folded up in its interior; magnified two diameters. 2. A portion of the Hectocotyliform arm, still further magnified: a, the sacculus laid open; 5, the arm, showing the commencement of the "lash," and also the suckers, nervous ganglia, &c.
(1610). Although we mean to defer any minute account of the development of the embryo in ovo until an examination of the eggs of oviparous Vertebrata shall afford more ample materials for elucidating this important subject, it will be as well in this place briefly to notice the condition of the young Cephalopods previous to their escape from the egg, wherein the first part of their growth is accomplished. Before the egg is hatched, the foetal Cuttle-fish already presents all the organs essential to its support and preservation: the tentacula upon the head, the eyes, the respiratory apparatus, and even the ink-bag, which in the earlier stages of growth were quite undistinguishable in the germ of the future being (fig. 303,1), slowly make their appearance; so that before birth the little creature presents most of the peculiarities which characterize the species to which it belongs. But the most prominent feature that strikes the attention of the physiologist is the remarkable position of the duct communicating between the yelk of the egg (the great reservoir of nourishment provided by nature for the support of the foetus whilst retained in the egg) and the alimentary canal of the as yet imperfect Sepia. This communication, which in vertebrate animals is invariably effected through an opening in the walls of the abdomen, whereby the vitelline duct penetrates to the alimentary canal, here occupies a very unusual situation, being inserted into the head, through which it penetrates, by an aperture situated in the front of the mouth, to the oesophagus, where it terminates (fig. 303, 3).