BUTTERFLIES OF TEE SEA. 



3S3 



organization and habit*, these little organisms 

 may be found to present some points of great 

 interest to the non-technical reader ; while to 

 the naturalist they have ever afforded subjects 

 of pleasant study and instruction. 



The position of the sea-butterflies in the ani- 

 mal scale is of sufficiently well-determined kind. 

 They are molluscous animals, that is, are allied 

 to our ordinary shell-fish, such as oysters, mus- 

 sels, etc., as well as to the cuttle-fishes and allied 

 beings. Their nearest relations are undoubtedly 

 the whelks, cowries, and other shell-fish, belong 

 ing to the great molluscan class known to natu- 

 ralists as the Gasteropoda ; and while some natu- 

 ralists regard the sea-butterflies as forming a 

 distinct group of themselves, others, and with 

 every show of reason, maintain that they should 

 be placed merely as a branch of the gasteropod 

 class. The scientific appellation of our sea-but- 

 terflies is the Ptcropoda — a name signifying 

 " wing-footed," and which is thus of expressive 

 enough kind, when we consider the manner in 

 which they flit over the watery wastes. 



Besides being able to swim quickly and w r ell 

 by aid of their wing-like fins, the sea-butterflies 

 can descend into the ocean-depths, or ascend 

 from these depths to the surface, at will. They 

 appear further to come to the surface chiefly at 

 night or in the twilight; and, as a naturalist has 

 well remarked, each species or kind of these ani- 

 mals seems to have its own and special degree 

 of darkness in which it ascends from the depths. 

 Thus, did we know sufficient of the history of 

 these little animals, we might be able to con- 

 struct a pteropod clock by watching the respect- 

 ive hours of their appearance at the surface 

 of the sea ; just as the botanist forms a " floral 

 clock " by watching the times of the opening and 

 closing of flowers. 



Being " shell-fish," the pteropods usually 

 possess a shell; this latter structure, it must, 

 however, be noted, not being developed in all 

 beings. A very beautiful and at the same time 

 most representative kind of sea-butterfly is that 

 known by the name of the Rt/alcea, of which kind 

 there are several distinct species ; and in this 

 form, as well as in another well-known species 

 called Clcodora, a shell is developed. The shell 

 is thus seen to consist of a very delicate, glassy 

 structure, somewhat triangular in shape, and of 

 elongated form in Cleodora ; that of Hyalsca 

 being composed of two plates united together, 

 and forming a small shell of elongated or globu- 

 lar shape. The little head-extremity of the ani- 

 mal, provided with its " wings," protrudes in 



each case from the front or open extremity of 

 the shell. Another very familiar sea-butterfly is 

 the Clio, which does not possess a shell, but ap- 

 pears as a little oblong body about an inch in 

 length, and terminating in a lower pointed ex- 

 tremity. 



No part of the structure of the sea-butterflies 

 presents more surprising details than that of the 

 head and its appendages ; the latter consisting of 

 tentacles, jaws, and like apparatus, exercising the 

 sense of touch and other offices. Thus, on each 

 side of the mouth of Clio, we discover three fleshy 

 appendages, which at first sight might appear to 

 consist of simple tentacles or organs of touch. 

 When, however, we bring the microscope to bear 

 upon these bodies, we note the interesting fact 

 that the surface of each is literally studded over 

 with numerous minute specks, which, when more 

 fully magnified, are seen to be of hollow cylindri- 

 cal shape, and to contain each about twenty little 

 suckers. These suckers may be protruded at will 

 from their respective cylinders, so as to constitute 

 an efficient apparatus for seizing and detaining 

 particles of food. Thus if we consider that each 

 of the six tentacles bears, on an average, about 

 3,000 of the cylindrical bodies, and that each of 

 the latter in turn contains about twenty suckers, 

 we reach the enormous number of 300,000 suck- 

 ers, as constituting the prehensile armament of a 

 single Clio, itself of very small size. And imagi- 

 nation may assist us in its scientific aspects bet- 

 ter than any other intellectual process, in endeav- 

 oring to form some idea of the extreme delicacy 

 of the muscles and structures whereby the protru- 

 sion and retraction of the suckers are secured. 



Two fleshy "hoods" serve to inclose the ten- 

 tacles when the latter are not in use and are re- 

 tracted ; and other filaments exist which may be 

 used to subserve the sense of touch in these 

 forms. Within the little mouth of the sea-but- 

 terflies, as also well exemplified in Clio, peculiar 

 jaws and a curious "tongue" exist, for the mas- 

 tication of food. Each jaw is a conical structure, 

 which literally bristles with sharp, spiny teeth ; 

 and the "tongue" is likewise studded over with 

 recurved hooks, which also aid in rasping down 

 or triturating the nutrient matters. And as com- 

 pleting the alimentary apparatus of the sea-but- 

 terflies, we find a well-developed throat, stomach, 

 a large liver, salivary glands, and other addenda ; 

 while a heart is also present, along with a system 

 of bloodvessels for the conveyance of the vital 

 fluid through the body. The breathing-organs 

 in some of these beings are well developed, and 

 appear in the form of delicate gills, or analogous 



