356 



INVERTEBRA TE MORPHOLOG T. 



closed. Suck cases are cylindrical structures with a double 

 wall, and are provided at one extremity with a somewhat 

 complicated apparatus for the ejection of the spermatozoa. 

 The exact method of their formation is not understood, but 

 apparently the seminal vesicles and the prostate play an im- 

 portant part in the process, the Needham's pouches being a 

 reservoir in which they may be stored up until required for 

 fertilization. 



Since the genital capsule is a portion of the viscero-pericardial cavity, 

 and the reproductive ducts are continuations of its walls, these structures 

 must also be regarded as prolongations of the enteroccel; and indeed second- 

 ary communications may exist between them and the viscero-pericardial 

 cavity proper. The genital capsule is not completely separated off from 

 the rest of the enterocoel, so that it might be possible for the reproductive 

 elements to pass from its cavity into the viscero-pericardial cavity proper, 

 and so to the exterior through the nephridia, though this method of exit 

 does not seem to be made use of. 



A remarkable modification of one of the armlike processes of the foot 

 occurs in the males of certain species in connection with reproduction. 

 The arm in Tremoctopus and PJiilonexis the third arm of the right side 

 of the body counting from the anterior mid line, in Argonauta (Fig. 158) 



A B 



FIG. 158. MALE OF Argonauta WITH HECTOCOTYLJZED ARM 

 (after H. MULLER from HATSCHEK). 



A = arm still enclosed within a membranous sac. 

 B = arm freed from the sac. 



the third of the left side is at first enclosed within a sac, by the 

 bursting of which it becomes free, the walls of the sac being reflected 

 back so as to form a pouch which in some unexplained manner receives a 



