634 PROFESSOE E. EAT LANKESTER. 



there is no suggestion of a nepliridium about the testicular sac 

 of Rhabdopleura. It belongs to that class of gonads (ovaries 

 and testes) which I have elsewhere ('Encycl. Britann./ art. 

 " Molluscaj" p. 682) distinguished as idiodinic (contrasted 

 ■with the nephrodiuic) . The Mollusca are in this case, whereas 

 the Polyzoa generally, the Brachiopoda, and the Sipunculoids 

 are nephrodinic. Too much importance must not be attached 

 to the isolated observation of these testes, but it will be a matter 

 of some significance if the ovaries should also prove to be sac- 

 cular, and provided with a duct-like continuation of their own 

 walls to the exterior. 



It seems to me probable that the '^cellular body" seen by 

 Sars near the rectum may be a gonad. The position of the 

 ripe testis, as now ascertained, is in favour of such an identi- 

 fication. 



SoFT-sTALK (Grymuocaulus), Hard-stalk (Pectocaulus), 

 Stalk-pipe (Caulotheca), and Bud-formation. 



In describing the general form of the tubarium I have already 

 indicated to a considerable extent the form of the colony of 

 polypides which inhabits it. We have just reviewed the structure 

 of a single polypide, with its long contractile stalk. How are 

 the various polypides connected which together make up the 

 colony ? The answer is simple enough. They are connected 

 by a branching stalk, which bears them upon it as an axis car- 

 rying appendages. This axial stalk branches from time to 

 time. The axial stalk is essentially the same thing 

 as the soft contractile stalk of a polypide. Every part 

 of it has in its time actually been the soft contractile stalk of a 

 polypide terminating a branch, and as the growth of the branch 

 has advanced the soft stalk has become gradually shrunk to a 

 narrow diameter, and has developed on its epidermis a hard, 

 firm cuticle, of a very dark-brown colour. At the same time 

 the cuticle, which thus- forms a narrow black pipe around the 

 shrunken stalk (^'the stalk-pipe" or '' caulotheca"), now rests 

 against the floor of the tubarium, and becomes adherent to 



