14 



In opposition to the Cheilostomata in which heterozooecia may also arise by a 

 process of budding from the surface of the zooecia (dependent heterozooecia) the 

 Melicerititidae only possess independent heterozooecia, and it is therefore a mistake 

 when Gregory in Foriciila aspera^) interprets a pair of long narrow pits seated on 

 each side of the aperture as avicularia. 



As a result of the above comparison I must agree with the opinion set forth 

 by Gregory^) that the avicularia in both divisions have developed independently, 

 and therefore are only parallel, not homologous structures. 



The Kenozooecia. 



Kenozooecia or bryozoids without an aperture (dactylethrae Greg) have been 

 found in 12 of the 31 species examined. As a rule they have the same form and 

 size as the zooecia, but as they lack an aperture they are provided with a uniform 

 flat or concave frontal area within the marginal ridges. In Mel. Steenstriiin they 

 are exceptional!}' much smaller than the zooezia. They are generally found inter- 

 spersed among the zooecia (pi. VI, fig. 19) in greater or smaller numbers, but in a 

 few species they take up together with a number of heterozooecia either the whole 

 "dorsal" surface or a large part of it (pi. Ill, figs. 11, 14), and at the whole they 

 are in most cases accompanied by heterozooecia, whether they appear in groups 

 among the zooecia or take up a large part of the surface of the colony. 



The Gonozooecia. 



The gonozooecia (pi. VII) which have hitherto only been found in a small 

 number of the species examined are zooecia provided with a large (1 — 2 mm. long), 

 more or less convex terminal expansion, an ooecium which in most cases has a 

 pyriform outline, but in the same species, nay in the same colony the form may 

 be subject to great variation, being sometimes roundedly triangular, sometimes 

 ovate or even circular. The distal end of the ooecium is provided with a trans- 

 versely ovate, somewhat infundibuliform, frontally directed aperture, and proxi- 

 mally it generally ends in a shorter or longer tail-shaped process. When the thick 

 porous frontal wall is removed, the flat or somewhat concave inner wall in most 

 of the ooecia examined presents a uniform smooth surface which is only inter- 

 rupted at the boundary between the caudal process and the rest of the cavity by 

 a rhombic zooecial area surrounded by prominent ridges and closed by a concave 

 calcareous film. Distally to this area which no doubt belongs to the gonozooecium 

 may sometimes be seen a few more or less indistinct rhombic impressions of the 

 same form and si/e as the zooecial areas, and when the inner wall of the ooecium 

 has been dissolved by the use of strongly diluted acid, there appears a mosaic 

 of rhombic zooecial areas each of which is closed by a concave calcareous film. 



') 14, p. 358. -I 14, p. 288. 



