ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 203 



spots. The larva is uniformly ciliated, and progresses actively over the 

 surface on which it occurs. It is not free-swimming, and rapidly sinks 

 to the bottom when placed in the water. It secretes a viscid substance 

 by means of which it adheres somewhat securely to the substratum. 

 The ventral surface has a thickened foot-like area. 



Sidney F. Harmer adds an appendix with particular reference to 

 recent literature not available to Gilchrist. He does not accept the 

 conclusion that " there is no evidence that the buds ever develop into 

 normal zooids, and that they may be individuals specialized for adhesive 

 purposes and coenoecium-building." The occurrence of almost innumer- 

 able individuals in a single colony almost necessarily presupposes that 

 the number of individuals increases by budding ; while Gilchrist's 

 observation that several zooids may occur in the individual coenoecial 

 tubes of C. (Idiothecia) gilchristi indicates, in all probability, that some 

 of the buds have assumed an adult character. 



A summary is given of the facts in regard to development which 

 seem to have been securely established. The egg of Gephalodiscus is of 

 considerable size — reaching a diameter of 680/* in Orthoecm .wUdus — 

 and it contains a large quantity of yolk. Segmentation is complete and 

 leads to the formation of a gastrula-like stage, although the mode of 

 origin of the inner layer has not been definitely established. The 

 lumen of the archenteron is very small, in correlation with the large 

 amount of yolk. The yolk is present in the cells of the inner and outer 

 layers in the earlier stages of development ; but it later disappears from 

 the outer layer, persisting in large quantity in a central mass representing 

 the wall of the archenteron, the cavity of which remains very small. 

 The wall of the archenteron is continuous with the outer layer, in the 

 later stages observed, near the posterior pole of the embryo. This 

 region may be regarded as the blastopore, and it seems probable that it 

 gives rise to the anus. 



The free-swimming larvae and the later embryos possess five body- 

 cavities arranged like those of the adult — namely, a large anterior cavity 

 and two pairs of clearly marked crelomic sacs, representing the body- 

 cavities of the collar and metasome respectively. These cavities are, 

 perhaps, developed as enterocoeles. 



A large area of the ventral ectoderm is much thickened and is occu- 

 pied with numerous gland-cells resembling those of the anterior or 

 " ventral " wall of the adult proboscis or buccal shield, and probably 

 gives rise to that part of the zooid. The anterior pole of the larva is 

 provided with a mass of clear vacuolated cells, situated in the ectoderm. 

 This organ is perhaps sensory. In G. indicus it has been shown by 

 Schepotieft" to bear a central tuft of long cilia and to be surrounded by 

 a circlet of smaller cilia. With the exception of the cilia just indicated 

 the larva is not known to carry definite rings of cilia, although part at 

 least of its ectoderm is uniformly covered with short cilia. The posterior 

 pole of the larva is generally provided with a definite ectodermic invagin- 

 ation of unknown nature, which has been called the " posterior pit." 

 The deeper parts of the ectoderm of the larva already show signs of the 

 development of a diffuse nerve-plexus. It appears improbable that there 

 is any pelagic stage and the observations of Andersson seem to indicate 

 that the larva becomes a zooid by direct metamorphosis. 



