276 ME. A. W. WATERS ON THE 



and contractile tissue (fig. 16). Then, again, in Smittia ophidiana 

 (fif. 15) the gland is as usual attached where the sheath joiua the 

 zocecial wall, but below it is fastened to the sheath and not to the 

 zocEcial wall. 



Since writing the above I have obtained Harmer's suggestive 

 paper * " On the Nature of Excretory Processes in Marine 

 Polyzoa," dealing with leucocytes and other cells. As many of 

 my slides bear interestingly on the subject I shall have to return 

 to the study of this point. However, if cells which wander 

 about in the zooecium become part of an encysted mass, as a 

 " brown body " which may or may not (perhaps after weeks or 

 months) be removed from the zooecium, ought we to compare this 

 with ordinary excretory processes ? 



Median Body. 



In ScMzoporella sanguinea there is another problematic struc- 

 ture which should certainly be studied in connexion with these 

 glands, as it arises very near to them, if not from the same tissues. 

 It hangs down from the opercular region, and when fully grown is 

 sausage-shaped, and ultimately may be said to be suspended by a 

 thin cord. This commences near the opercular opening, at first 

 simply as a projection of the tissue, afterw^ards forming a thin 

 lancet-like pendant, which gradually increases in thickness. Of 

 course in all these calcareous species it will never be possible to 

 follow the growth of any individual, and it is only by seeing a con- 

 siderable series in decalcified preparations and sections that the 

 growth can be worked out. 



Tiie whole body is surrounded by a membrane, and in the 

 contents there are irregular-shaped strongly refractive masses, 

 which appear homogeneous and do not stain (PL XIX. figs. 9-12). 

 Eound each of these refractive masses there is a clear space, 

 and the general appearance of the whole structure would suggest 

 that it is connected with reproduction, and w-e must ask whether 

 it is to be compared with seasonal eggs. There is sometimes an 

 ovarium in the same zooecium as these sausage-like bodies. 



In Diaclioris magellanica^ Busk, the so-called eggs (JuUien) 

 have at the commencement a minute structure similar to 

 that of the sausage-shaped bodies in ScMzoporella sanguinea. 



* Micro. Journ. vol. xxxiii. n. s. p. 123. 



