THK STING -RAY. 



43a 



of the tissues whicli occupy the lateral grooves, which for con- 

 venience and brevity I propose in future to speak of as the 

 glandular triangle (Porta spe;vks of it having a triangular shape 

 in section with the angles rounded oif), we must study sections 

 at the root of the spine or dart, before it separates from the whip- 

 like tail. With the naked eye one can see a special dai-k pig- 

 mented patch on the tail where it opposes the spine, on the 

 surface of which appears some soft whitish epidermis. More- 

 over, if we view the spine at this point in profile, we notice that 



Text-fio-ure 1. 



c.o.y. 



Trygon pastinaca. 



Part of gland in groove. 



c.c.g. Central canal of groove, c.f. connective tissue, e.g. epithelium of groove^ 

 f.g. follicles of gland, o.p.s. osseous part of spine, p.l. pigment-layer^ 

 v.a.g. ventral aspect of groove. 



the dorsum of the spine becomes free of the epideimis which 

 has been covering it sooner than the ventral aspect, so that the 

 dorsum of the spine in this respect is somewhat similar to the 

 nail on a man's finger. The epidermis ends rather abruptly on 

 the dorsum, while, on the other hand, the dentate margin and 

 the lateral grooves between it and the ventral ridge separate 

 gi-adually from tine tail, the last part to become free being the 

 ventral ridge. On either side thei-e is a gradual invagination 

 of ectoderm between the tail and the glandular triangle, this. 



