164 THE SPINY DOGFISH -THE SKATE 



Note that only vestiges of the Miillerian ducts are present in the male. 

 Notice the associated copulatory claspers of the pelvic fins. 

 Dissect away the sperm-sac to show the vesicula seminalis. 

 Make a drawing of the male urino-genital system. 



OEsophagus cut through-^ 



'-Shell gland 



Vas deferens-- 



Kidney 



Vesicula seminaliS' 



Opening of 

 Vesicula seminalis' 

 [Urinary papilla 

 -Pelvic girdle cut througb-y— -vSjM 



"J" -Abdominal pore 



Fk;. 54.- 



-The Dogfish (Acanthias, syn. Sqtialus). A. Urino-genital system of the female ; 

 B. the male. 



C. The Skeletal System (part). 



Remove the skin and muscles from the region between the pectoral fins, and 

 clean the base of a pectoral fin and the pectoral girdle to show the skeleton. 

 Make a drawing to show the following parts : — 



1. The Pectoral Girdle. 



This consists of a hoop of cartilage incomplete dorsally. Its thick ventral 

 portion represents the coracoid, each side of which bears three articular (glenoid) 

 facets for the three basal pieces of the pectoral fin. The incomplete dorsal 

 portions of the girdle represent the scapula. 



2. The Pectoral Fins. 



Each fin articulates with the pectoral girdle by three basal pieces of 

 cartilage — the very small propterygium, the mesopterygium, and the large 

 metapterygium. The propterygium and the mesopterygium each bears a 



