NO. 1816 STORY OF THE DEVIL-FISH — GILL 175 



EXPLANATION OF FIG. 54. 



1. Embryo of Pteroplata:a micrura, from dorso-lateral aspect; nat. size, but 



with only a few of the gill-filaments represented, for the sake of clear- 

 ness, s, spiracle. 



2. End of a gill-filament, showing marginal capillary filled in places with 



blood-clot. X 42. 



3. Transverse section of a gill-filament, showing the marginal capillary in 



section and the single fold of epithelium. X 188. For the sake of clear- 

 ness the blood-clot is represented in one limb of the capillary only, and 

 the spaces between the nuclei of the surface epithelium are a little 

 exaggerated. 



4. End of a trophonema, or nursing-filament, seen as a transparent object in 



glycerine, showing the marginal artery and the superficial capillary 

 plexus. X 42. The median vein is not seen so near the end. 



5. Obliquely transverse section through a nursing-filament, showing the glands 



still in the form of solid bulbs lying beneath a still unbroken surface of 

 epithelium. X no. aa, arteries; v, vein; cc, superficial capillaries. 



Doubtless an analogous provision for the nutrition of the embryo 

 is developed in the Devil-fishes, and thus we have a satisfactory ex- 

 planation of the statements of Patchen and Mitchill. Something 

 like milk is secreted by the mother fish and is ingested by the young, 

 but it is chemically different from milk, and instead of being sucked 

 in by the mouth is absorbed through the postocular spiracles. The 

 statements which have been much ridiculed have therefore a sound 

 foundation in fact and are susceptible of a natural explanation. 



Nothing is known respecting the development of the embryo of 

 any Devil-fish, but undoubtedly it is similar to that of the Sting-rays. 



The very young embryo of the Sting-rays, as of all other Rays, 

 contrasts remarkably with the mother, especially in the case of the 

 very wide forms, such as the Pteroplateines. The embryo at an 

 early stage has a form very like that of a Shark, but with pectorals 

 provided with basilar extensions free from the head, and extending 

 forward parallel with it in advance of the eyes. These extensions 

 later unite with the sides of the head, and the regular Ray has then 

 become developed. Essentially, the form of the mother has been 

 attained by the young when ready for extrusion from the mother's 

 womb. This much at least is known of the new born of Devil- 

 fishes, 



VIII 



The various species of Devil-fishes are representatives apparently 

 of three different generic types, distinguished by differences of deri- 

 vation. Mobula (also called Aodon, Cephaloptera, or Diccrobatis'. 



