758 SIPHUNCLE AND PALLIAL VESSELS. 



essentially as the siphuncular artery. This arises indifferently from either the right or 

 the left of the two principal branches. Owen (1832), Valenciennes (1841), Vrolik (1855), 

 and Haller (1895) have described what I have called the posterior pallial artery as 

 passing direct to the siphuncle. Keferstein (1865) with more accuracy said that it 

 passes " nach hinten zur Korperhaut und besonders zum Sipho." Injections show that 

 the siphuncular artery is simply on a par with the other ramifications of the posterior 

 pallial artery, the ultimate branches of which constitute a remarkably rich system of 

 irrigation for the septum-producing area of the mantle. 



Before continuing my account of the pallial arteries it will be convenient at this 

 point to complete what I have to say regarding the connections of the siphuncle. 

 Owen, as I have already mentioned above, described a direct communication between 

 the pericardial cavity and the siphuncle, saying (memoir, p. 27): — "by the side of this 

 vessel " [the posterior pallial artery] " a free passage is continued between the gizzard 

 and ovary into the membranous tube or siphon that traverses the divisions of the shell ; 

 thus establishing a communication between the interior of that tube and the exterior of 

 the animal" [through the viscero-pericardial apertures]. 



Valenciennes (1841) denied any communication between the siphuncle and the 

 exterior through the mediation of the pericardium, and further affirmed that it did not 

 even open into the abdominal cavity at its base. Vrolik (1855, p. 7) said that 

 Valenciennes was wrong, " car, d'apres ce que j'ai vu, le siphon s'ouvre dans la cavity 

 abdominale, comme la pi. I., fig. 5 c le demontre." But on turning to the figure referred 

 to we find that it is by no means demonstrative in this respect. Vrolik was confident 

 as to the actuality of his observations, and stated in a foot-note that he had shown 

 his preparation to many foreign anatomists, including Kolliker, who mentioned it among 

 the impressions of his travels in his Zeitschrift. It is no light matter to attribute an 

 error to an anatomist of Vrolik's reputation, especially since he alludes at another part 

 of the " Lettre " from which I am quoting to " l'erreur grossiere de voir des ouvertures 

 la ou elles ne sont pas." Nevertheless I shall proceed to show that he was wrong in 

 this matter in spite of the asseverations of Keferstein (1865) and Haller (1895). 

 Keferstein 1 defines the siphuncle in these words : — " Der Sipho ist hinten eine rohrige 

 Fortsetzung der Korperhohle, wircl der ganzen Lange nach von einer Arterie durchlaufen 

 und muss grade wie die Intervisceralraume des Korpersackes venoses Blut enthalten 

 konnen." 



It is true that in addition to its main artery, the siphuncle is traversed by a wide 

 axial cavity, and it is perhaps to be inferred from Keferstein's definition that this axial 

 cavity of the siphuncle is a continuation of the abdominal or perivisceral cavity in 

 which the gonad and other viscera lie, in other words that it is part of the secondary 

 body-cavity or coelom. But whatever inference may be drawn from somewhat vague 

 statements, we find precise assurances on this subject in the recent memoir of Br Haller 

 (1895, p. 201), who says: — "Der Sipho communicirt direct mit dem grossen Colomraum, 

 und zwar, da sich tiber ihrer Mundimg der ventrale Theil des Genitointestinal-ligamentes 

 an die hintere Wand des Coloms befestigt, scheinbar mit zwei Oeffnungen, thatsachlich 



1 Nachr. Ges. Gottingen 1865, p. 369. 



