SEXUAL CHARACTERS ELASMOBRANCH FISHES 373 



glands, while having a physiological function analogous to a 

 prostate, cannot be homologous with the gland called prostate 

 in man, but may rather be homologous^ with the group, called 

 Cowper's and Bartolini's in human anatomy, whose function is 

 at present problematical. 



Lamna is generally described as possessing open spiracles but 

 I failed to find them, my experience agreeing with that of Glinther 

 before me. There is a deep hyomandibular cleft, but no perfor- 

 ation pierces the skin. 



I have discovered in Lamna a large much-coiled infra-orbital 

 gland to be described elsewhere. 



RHINA SQUATINA 

 The monk or angel-fish 



The specimen of Rhina upon which the following examination 

 was conducted, taken at Plymouth in January, 1919, measured 

 29 in. from the tip of the snout to the extremity of the body 

 (the cleft in the heterocercal tail), exclusive of the caudal fin. 

 Here again the claspers are small in proportion to the size of the 

 animal, being very slightly shorter than the pelvic fins, and 

 measuring but 2 cm. 



The monk fish was long considered a connecting link between 

 the Selachoidei and the Batodei, though I believe this view is 

 no longer held by morphologists. As regards the claspers, etc., 

 it agrees with the skates rather than with the sharks. 



The claspers are soft and smooth, and devoid of denticles, as 

 in Raia. They taper to a fine point. There is no trace what- 

 ever of an apopyle. The tube leading from the siphon does not 

 extend to the extremity of the clasper as in Raia. Instead of 

 possessing large siphons of the type found in Scyllium and 

 Galeus, it resembles Raia, or more closely Lamna, in having a 

 short clasper gland, in this case 3 cm. in length (fig. 10). 



Jungersen in 1898 discusses at some length this gland which he 



3 Possibly 'homoplastic' would be a clearer expression to indicate parallel 

 development. 



