THE PAST AND PRESENT OF THE CUTTLEFISHES. 87 



cuttlefish head as its lower, and of its tail as its upper, extremity, is a 

 correct zoological designation, we must enter upon a comparison of 

 the cuttlefish body with the forms of its neighbour molluscs. The 

 contemplation of such a familiar being as a snail or whelk, intro- 

 duces us to a characteristic example of molluscan form and anatomy. 

 The head of the snail or other gasteropod is clearly enough defined ; 

 and no less plainly discernible is the enlarged and broadened sur- 

 face on which the animal walks. This surface is known as the 

 "foot." In one shape or another, this "foot" is a characteristic 

 possession of the molluscan tribes. In a section of a mussel or 

 cockle, we perceive the " foot" to exist as a muscular mass developed 

 in the middle line of the body below, and variously used in the 

 mussel-class as a spinning organ, a leaping pole, and a boring 

 apparatus. Here we note the natural development of the foot in the 

 middle line of the animal. Let us suppose this foot to be extended 

 downwards, and to be broadened so as to form a surface of progres- 

 sion, and we may conceive readily of the modification whereby a 

 simple foot like that of the mussel becomes developed to form the 

 enlarged disc of the gasteropod. In the latter case, we observe that 

 the foot occupies the floor of the body ; the bulk of the body, and 

 the head in particular, being borne above. 



Cuttlefish development can be shown to run, so far, in parallel 

 lines to those of the personal evolution of mussel and snail. But 

 divergent paths soon appear in cuttlefish development ; and these 

 variations, whilst they indicate an ancient departure from the ordi- 

 nary molluscan type, likewise give to the subjects of our present 

 study their most characteristic features. When a mussel or snail is 

 watched in its earlier stages of development, the embryo is seen, 

 sooner or later, to produce an appendage highly characteristic of 

 molluscan young at large, and named the velum. By aid of this 

 ciliated fold, such an organism as a young cockle, for instance, swims 

 freely through its native waters. This velum undergoes varied 

 changes and alterations in the after stages of molluscan develop- 

 ment ; but when cuttlefish development is studied in its fullest 

 details, no velum is found amongst the possessions of the larval 

 body. Such an omission has naturally been made the subject of 

 remark by naturalists. Some authorities Grenacher, for instance 

 have insisted upon the recognition of the arms of the cuttlefish head 

 as the representatives of the missing velum. But as the latter organ 

 always exists on the dorsal or upper side of the mouth, and as the 

 arms are placed originally behind and under the cuttlefish mouth, the 

 correspondence of arms and velum has not been accepted by zoolo- 

 gists. On the other side stands out the opinion of Huxley, who 

 regards the " arms " of the cuttlefish head as more truly correspond- 

 ing with the " foot " of the mussel, snail, and other molluscs. 



