454 



NA TURE 



[August 29, 1907 



These schemes are not entirely satisfactory. Certain 

 difficulties are common to them both. The posterior 

 salivary glands, which, it is assumed, were inherited in a 

 fused condition from the primitive Qigopsid stem, and 

 remain in that condition in Hossia, have been separated in 

 IJiosepius, Sepiadariiim, and Sepiola, as well as in Sepia 

 and Loligo. 



Furthermore, A presents the difficulty that the fusion of 

 the mantle with the head in the nucha! region has been 

 acquired independently by hUosepius, Sepiadariiim and 

 Scpioloidca, and Sepiola. 



On the other hand, B has the disadvantage of assuming 

 that the hectocotylisation has been transferred from the 

 fourth to the first pair of arms independently in liossia and 

 Sepiola. 



If, as I believe to be the case, scheme A is admitted to 

 offer the lesser of the two difficulties, it has the advantage 

 of indicating that the hectocotylisation of the ventral arms 

 has been directly inherited from the main stem common 

 to Myopsids and CEgopsids, and has only been transferred 

 to the dorsal arms in the branch common to Rossia and 

 .Sepiola. 



Hence we reach the conclusion that, although the 

 variations in the structure and position of the hecto- 

 cotylus follow pretty closely the systematic divisions of the 

 Dibranchiata, we are not justified in maintaining that the 

 position of the hectocotylised arm is by itself a sufficient 

 guide to the systematic position of a doubtful form ; it is 

 only one of many characters that must be taken into 

 consideration. 



The subject of fossil Cephalopoda has not formed any 

 part of my own special researches, but a contribution has 

 recently been made to our knowledge of these forms to 

 which it seems desirable to allude, because it deals, not 

 with systematic or stratigraphical facts, but with con- 

 clusions which may be drawn from shell structure as to 

 the life-history and habits of certain important and interest- 

 ing forms. Prof. Jaekel, formerly of Berlin, now of 

 Greifswald, the author of the memoir referred to, lays down 

 a number of theses regarding the organisation and mode 

 of life of these e.xtinct species, and I venture to give an 

 abstract of his views, premising that my acquaintance with 

 paleontology does not justify me in expressing a definite 

 opinion as to the validity of his conclusions, though they 

 seem extremely reasonable. 



His opening statement is that Orthoceras and its allies 

 were not free-swimming but sessile organisms, and this is 

 based on the following arguments amongst others. The 

 shells were thicker and heavier than any that are found 

 in pelagic organisms ; the external sculpture shows that the 

 shell was not embedded in the soft parts, and if it were 

 exposed the annulate arrangement of many forms is incon- 

 sistent with their easy passage through' the water; the 

 " lines " (in the naval architect's sense of the word) of an 

 organism intended for navigation are always smooth and 

 not wavy; otherwise undue friction against the water would 

 be created ; whilst the straight transverse margin of the 

 aperture of the shell shows that it was not carried by a 

 creeping body like that of a snail. Their sessile nature is 

 further shown in the first place by the radial symmetry, 

 which is rare in free-swimming forms, and almost unknow-n 

 in those the axis of which is long in proportion to their 

 diameter. Further, the termination of the shell is generally 

 broken off : of all the thousands of specimens which have 

 been examined, but very few show the initial chamber ; in 

 those cases in which the apex is preserved it shows a 

 scar, where the siphuncle entered the protoconch. The 

 separation of the shell into chambers by transverse 

 septa occurs only in sessile forms, but in such it is 

 found in many divisions of the animal kingdom. The 

 reason of this cameration is to be found in a constant 

 effort to keep the body of the animal above the surface of 

 the mud in which it is rooted. On this view the siphuncle 

 admits of a simple explanation ; it is the vestigial part 

 of the body which has been contracted and partially cut 

 off as the body has moved successively forward to the 

 enlarged superior portion of the shell. 



It may be added that J. M. Clarke has recorded a case 

 in the American Upper Devonian rocks in which the 



majority of the large Orthoceratida^ were fossilised in a 

 vertical or but slightly sloping position. 



The forms such as Phragmoceras, &c., in which the 

 aperture of the shell is contracted, and often shows 

 bilaterally symmetrical notches, are interpreted as having 

 lived buried in the mud. The notches served for the 

 protrusion of the anus, vent, and siphon, which latter 

 were probably elongated tubes stretching up through aper- 

 tures excavated in the mud, much in the same way as the 

 heart-urchin {Echinocardiiiin) among the sea-urchins lives 

 buried in the mud, and obtain.s nourishment by stretching 

 its tube feet up to its surface. The arrangement of the 

 arms was probably like that seen in the embryos of Di- 

 branchiata, or of the circunioral appendages of Nautilus. 



Turning to the extensive and interesting group of 

 Belemnites, Prof. Jaekel enunciates the view tnat these 

 were not, as has been commonly believed, active free-swim- 

 ming forms, the rostrum (guard) serving as the pointed 

 ram of a battleship, but stationary, the rostrum playing the 

 part of a pile by which they were rooted in the mud at the 

 sea-bottom, like the pointed base of a Flabellum cr other 

 deep-sea coral, or thr- anchor-spicules of a glass-rope sponge. 

 In favour of this view may be adduced the size, weight, 

 and solidity of the rostrum, which, if the animal moved 

 about in a horizontal attitude, would have thrown its 

 centre of gravity too far towards that end of the body : 

 its circular section, which points lo a radial, not a bilateral, 

 symmetry, and hence, as above mentioned, to a sessile 

 rather than a free-swimming habit. The pointed form of 

 the rostrum would be admirably adapted to fixation in 

 a muddy bottom, whilst its weight would render it a very 

 effective anchor. Further, it is to be noted that Belemnites 

 are found abundantly in strata of argillaceous origin. 



This view has a strong recommendation in the fact that 

 it presupposes gradual progress in the Cephalopoda in the 

 direction of greater mobility as evolution advanced, thus : 



.'\. Orthoceras — firmly attached. 



B. Belemnites — anchored in the mud. 



C. Recent Dibranchiata — free-swimming. 



Another interesting discovery of Prof. Jaekel is that 

 of a slab of Solenhofen stone, upon which are certain 

 specially arranged impressions, apparently made by the 

 hooks on the arms of a Cephalopod. If this determination 

 is correct, the fact is of the greatest interest, for it would 

 show that these animals walked upon the ground with the 

 head downwards and the distal extremity of the body ele- 

 vated ; that in them the arms were not merely morpho- 

 logically, but also functionally, the equivalent ot a foot. 



In conclusion let me direct your attention to a subject 

 which is almost entirely the growth of the last fifteen 

 years. I mean the discovery and investigation of luminous 

 organs in the Cephalopoda. These have now been ob- 

 served in no fewer than twenty-nine out of about seventy 

 well-characterised genera of Decapoda, and have been found 

 to present a most interesting variety in position and in 

 structure. 



Before passing on, however, to consider the structure 

 of these organs, it may be well to lay before you the 

 evidence on the strength of which a photogenic function 

 has been ascribed to them. The actual observations are 

 remarkable chiefly for their paucity ; indeed, it may seem 

 to some that the foundation of solid fact is too slender for 

 the superstructure raised upon it, but still due consideration 

 will show that this is not the case. The first recorded 

 occurrence of phosphorescence in the Cephalopoda is due 

 to V^rany, and dates back rather more than seventy 

 years, though it was not published till 1851. The descrip- 

 tion is so definite and concise as to be well worth quoting : 



" As often as other engagements permitted, I watched 

 the fishing carried on by the dredge on the shingly beaches 

 which extend from the town of Nice to the mouth of the 

 \'ar. On the afternoon of September 7, 1834, I arrived at 

 the beach when the dredge had just been drawn in, and 

 saw in the hands of a child a cuttle-fish, unfortunately 

 greatly damaged. 1 was so struck by the singularity of 

 its form and the brilliance of its colour that 1 at once 

 secured it, and, showing it to the fishermen, asked whether 

 Ihev were acquainted with it. Upon their replying in the 



NO. 1974, VOL. 76] 



