1884.] 83 [Hyatt. 



that these invaginations occur as figured by Barrois, and that the 

 threads are surrounded by a perifibral membrane, the cells 

 being similar to those of the ectoderm and continuous with 

 them. This perifibrum envelopes the spicules as well as the fibre 

 and leaves no doubt that they are all inclosed, but whether the 

 epidermal cells give rise to the spicules we could not ascertain* 

 though this was an almost necessary inference from our observa- 

 tions and those of Barrois'. The cells of the perifibrum as 

 observed in Halichondria and Chalinula were very long, fusiform 

 and flat, and though occasionally loaded with granules were never 

 gibbous or similar to the spongoblasts of Schultze, which should, 

 we think, be styled keratoblasts. A similar membrane has 

 been discovered by Von Lendenfeld in Apiysina, and described 

 in his papers on Australian Sponges. Oscar Schmidt has given 

 the best figures of the spicules in their early stages in a larva of 

 Esperia (Zeitschr. Wissen. Zool., vol. xxv., supplem. pi. 10.) Such 

 observations have been generally considered as confirmatory of 

 the views that the collar is mesodermic, but in our opinion it 

 shows simply that invaginations of the outer layer of the body 

 may have similar functions, whether occurring in the embryo 

 or in the adult. Such invaginations may be expected to build 

 either spicules, or keratode, or both, in varying proportions 

 according to the hereditary form and needs of the sponge. 

 Thus the gastrula not only serves to place the endoderm in posi- 

 tion, but also builds the plug in the narrow neck of which is 

 formed the fan-like fascicle of spiculr s or threads commonly 

 found in the cinctoplanuki, and afterwards apparently dispersed 

 in the mesoderm, though always we think surrounded by the 

 perifibrum. 



The variability of shape in the collar and its large size in Car- 

 neospongiae, and the stiff setae, suggest that it may be an 

 organ destined to assist the ovum in freeing itself from the tough 

 membranous envelope. Though no author has observed a chorion 

 in the Calcispongiae, it is very probable that the " Deckzelle " of 

 Polaejeff is the chorion, or its homologue. Whether it is tough 

 or not we do not know, though it is plain that the ovum breaks 

 out of the chorion, as a rule, at an earlier stage than among Car- 

 neospongiae. The occurence of caleareous shells in the ova of 

 Sycaltis testipara, Haeckel, Caleispongiae, vol. h, p. 271, pi. 47, 



