VIVIPAROUS RAYS 211 



in shallow little tidal pools lying behind natural break- 

 waters of sand, and it seemed as if this comparatively 

 safe situation had been deliberately chosen by the 

 mother as a nursery for her expected family, as in 

 the opinion of Professor M'Intosh is the case with the 

 viviparous Blenny of northern seas. 



Females of the short-tailed bat-ray {Pteroplatcea 

 micrura) in all stages of pregnancy were found, the 

 most interesting of all the specimens being one con- 

 taining an embryo about li inches long, still attached 

 to a yolk-sac full of unconsumed yolk. Regarding this 

 embryo two facts of very considerable importance were 

 elicited, one relating to the yolk-sac, the other to the 

 embryo itself. With respect to the yolk-sac and its 

 stalk, the noteworthy feature was that they contained 

 no blood-vessels for absorbing the yolk, such as are 

 generally found in all yolk-sacs, and yet the yolk was 

 being consumed, for small particles of it were found 

 passing along the hollow of the stalk of the sac into 

 the embryonic intestine into which the stalk opens ; 

 besides which, the whole yolk-sac was enveloped in a 

 cloud of long, vascular filaments springing from the 

 gill-clefts of the embryo, and to these external branchial 

 filaments no other function could be assigned than that 

 of absorbing the yolk in some way. The little embryo 

 also revealed some interesting secrets of its own gene- 

 alogy. It was shaped not like a skate, but more like a 

 shark, having a shark's snout and a shark's tail ; like a 



