84 SYNOPTIC COLLECTION. 



First : Duration of the furrowing period, thirty hours. 

 Second: Swarming out of the larvae, continuing to the 

 end of the second day. Third : Free-living larva stage 

 during third, fourth, and fifth days. Fourth : Settlement 

 on fifth day. Fifth : Formation of the ampullaceous sacs 

 and of the body cavity on the eighth day. Sixth : Break- 

 ing through of the cloacal opening and the formation of 

 the skin pores. 



According to Dendy l the West Indian Chalininae 

 offer the strongest arguments in favor of the view that 

 the Keratosa have descended polyphyletically from sev- 

 eral distinct groups of silicious sponges. In different 

 species of the same genus he has traced the gradual 

 reduction and disappearance of the spicules until forms 

 are reached like Spinosella maxima Dendy, and Spinosella 

 plicifera D. & M., which sometimes still contain traces of 

 the spicules imbedded in the horny fiber, and apparently 

 on the verge of disappearance, while at other times they 

 contain no spicules whatever, and yet the specimens with 

 spicules and those without are specifically indistinguish- 

 able. No. 86 Tuba (= Spinosella' 2 ) vaginalis Lam. var. 

 sororia, and No. 87, Tuba scrobiculata D. & M., show the 

 variation in form peculiar to this genus of sponges. 



KERATOSA. 



The Keratosa are not found in a fossil condition. 

 They are probably the specialized descendants of silicious 

 forms, some of which have already been described. 

 This view finds additional confirmation in the researches 

 of Maas 8 who states that the embryological development 



1 Trans. Zool. Soc. London, XII, part 14, 1890. 



2 Vosmaer in 1885 substituted the generic name of Spinosella for 

 the familiar one of Tuba. 



3 Zool. Jahrb., Anat., VII, Heft 2, 1893, p. 331. 



