STBUCXUB.E OF THE MAEIXE POLTZOA. 7 



(if we except the oldest or basal member and the youngest or ter- 

 minal) there spring in regular order lateral shoots, by which the 

 stolon sends out on one side a series of filiform zooids like those 

 of which it is itself composed, and on the other the zooids which 

 form the flask-shaped or nutritive members of the colony. Each 

 component member of the burrowing stolon may thus carry on its 

 distal end two opposite zooids, one of which is a filiform zooid, 

 the other a nutritive zooid. 



The filiform zooids push themselves between the layers of the 

 tube-wall of the Annelid ; the nutritive zooids, on the other hand, 

 perforate the inner layer, forming a circular orifice through which 

 the animal projects its crown of tentacles into the lumen of the 

 tube. 



The component members of the stolon are dilated at their distal 

 ends (where they carry the two opposite zooids) into a kind 

 of flattened capsule. In the rest of their extent they present, 

 under a low magnifying power, an obscurely ringed appearance. 

 Each forms a completely closed tube filled with a clear non-cor- 

 pusculated liquid. The wall is composed of a laminated chitinous 

 ectocyst lined by a soft endocyst *, in which granules and fusi- 

 form nuclei lie embedded, but which shows no differentiation into 

 distinct cells. In the capsule-like dilatations there occur peculiar 

 structures in the form of glistening, thin, straight bands, which 

 are stretched from one side of the capsule to the other, and at 

 their points of attachment pass into the protoplasmic substance of 

 the endocyst. Each of these bands contains a very distinct nu- 

 cleus, but shows no further differentiation. They closely resemble 

 muscular fibres such as are developed in the nutritive zooids; but 

 Ehlers could obtain no evidence of contraction. 



Unlike the filiform zooids, the nutritive zooids possess in most 

 respects the typical structure of a Gymnolsematous polyzoon. A 

 peculiarity by which they are characterized consists in the pre- 

 sence of two hollow horn-like processes, which arise, one on each 

 side, a little behind the orifice of the zocecium. Nothing can be 

 asserted as to the significance of these processes. Their cavity 

 does not appear to communicate with that of the zocecium. 



The body-wall of the nutritive zooids consists of the same layers 

 as that of the filiform zooids ; the endocyst, however, is seen to 



* Ehlers, on grounds which cannot be regarded as sufficient, refuses to 

 employ the terms "ectocyst" and "endocyst," as well as "polypide," "zoce- 

 cium," and others now generally accepted by writers on the Polyzoa. 



