374 W. HAROLD LEIGH-SHARPE 



calls the 'glandular sac' According to him, the sac is so large, 

 standing out in relief under the skin, that he compares it with 

 the calf of a man's leg. He does not state the size of his fish, 

 and the circumstance that no such raised appearance of the sac 

 was visible in my specimen may have been due to its smaller size 

 or to the absence of much secretion. In this connection it is 

 interesting to note that this author states that the glandular sac 

 is full of mucus, and my investigations show that the gland of 

 Rhina is simply and solely a mucous gland (fig. 8, C). It is 

 unfortunate that the investigator, though perfectly correct in 



Ventral . Dorsa 1 . 



Fig. 10 Rhina squatina. Cl.Gl., clasper gland 



this instance, should have been led to generalize that clasper 

 glands are always mucus-secreting for in its histological struc- 

 ture the gland of Rhina differs from that of Lamna and Raia. 

 f^^^The gland arises as epidermal patches, and is at first super- 

 ficial at or near the point where the clasper adjoins the pelvic 

 fin. More anteriorly, glandular tissue surrounds the imper- 

 fectly closed tube of the clasper and finally becomes a completely 

 closed gland surrounding a lumen. These gradual transitions I 

 have endeavored to diagrammatize in figure 12 from various 

 selected transverse sections. In these sketches the supporting car- 

 tilage is black ; the small circles indicate sporadic masses of blood 

 corpuscles marking the presence of erectile tissue; the dotted 

 portions reveal the glandular tissue. I and II are across the 

 clasper. The cartilaginous skeletal support is a single rod, 

 erectile tissue is present, but as yet no gland. 



