250 MORPHOLOGY OF INVERTEBRATE TYPES 



incision a little to the left of and parallel with the median line 

 of the lower surface. This incision should extend throughout 

 the entire length of the mantle and care must be taken not to 

 injure the organs. Place now the squid with its head away 

 from you, press the sides of the mantle apart and fasten them 

 firmly down with pins, thus exposing the mantle cavity. The 

 funnel appears now as a hollow and somewhat flattened muscular 

 cone, open at both ends. The two long, grooved cartilages of 

 the funnel the infundibular cartilages are now naturally sep- 

 arated from the pallial cartilages of the mantle with which they 

 articulate. The sides of the funnel are provided with muscular 

 valves one on each side which have the appearance of flaps. 

 The two heavy muscles arising from the sides of the funnel and 

 running parallel to each other are the retractors of the funnel. 

 The two plume-like organs situated to the outside of the retrac- 

 tors and attached to the mantle by a sheet of integument are 

 the gills or ctenidia. The vessel running along each gill is the 

 branchial vein. The single organ lying in the median line be- 

 tween the retractors of the funnel is the rectum. The anus opens 

 into the funnel and on its sides are the two rectal papilla. From 

 now on the description varies according to the sex of the spec- 

 imen. In case of a female proceed to instruction No. 16. 



Male. In case the specimen is a male it can be recognized 

 as such by the presence of the penis at the left side of the rectum 

 (on your right). Under the rectum the sides of the iridescent 

 ink-sac are visible. The round bodies, one at the base of each 

 gill, are the branchial hearts. A small gill muscle arises from the 

 base of each gill and terminates in the mantle. The vessel 

 running from the mantle to the branchial heart on each side and 

 in its course more or less parallel to the gill, is the mantle vein. 

 The two large, bluish, semitranslucent vessels running obliquely 

 from the branchial hearts backwards, are the posterior vena cava. 

 Three smaller vessels arise from a median point between these 

 veins. They are the mantle arteries. Of these the two lateral 

 mantle arteries accompany the posterior venae cavas. The 



