364 CARL VOGT. 



tions are correct, differs widely from the species described by that 

 author. 



Sexual individuals, both male and female, are found on the 

 same Phascolosoma, but the tufts (or colonies) are to a great 

 extent either male o/- female. The female tufts may be recognised 

 at once under the lens by the masses of white ova, whilst the 

 male are composed of a multitude of transparent individuals, 

 with only here and there a white point. The colonies are, there- 

 fore, in great part, but not absolutely, unisexual. Whilst a 

 large proportion of the polypides in a tuft are of one sex, there 

 are always a few individuals amongst them of the opposite sex. 

 The clustered ovisacs, situated at first on each side of the intes- 

 tine, but which are pushed Httle by little into the vestibule, are 

 analogous to the incubation-pouch {die Bruttasche) of the 

 PedicelUnce, described by Nitsche, with this difference, that the 

 latter exists from the first and possesses very thick walls, whereas 

 the ovisacs of Loxosoma are always very thin, and are developed 

 gradually as the eggs increase in size. 



The Ova and Larv^. 



The Author proceeds to trace the development of the ovum 

 through its various stages. After the commencement of segmen- 

 tation the granulations become more and more opaque, the eggs, 

 viewed by direct light, present a chalky appearance, and nothing 

 but the outlines of the vitelline mulberry masses are distinguish- 

 able. The Author was able to make out the commencement of the 

 segmentation, marked by the appearance of two transparent nuclei 

 in the (as yet) undivided vitellus ; but the subsequent stages he 

 was unable to follow, though the progress of the segmentation 

 was indicated by the increasing number of nuclei, which were 

 visible in the ovum when submitted to compression. By the 

 same means he was able to determine that the cells situated at 

 the centre had become more opaque than those at the circum- 

 ference — a proof that the differentiation into ectoderm and 

 endoderm had taken place. The opacity of the ova, which yielded 

 to no reagents, prevented him from traciug in detail the forma- 

 tion of the gasirula. 



M. Barrois seems to have succeeded better.^ He states that 

 development proceeds with perfect regularity up to the 8-segmen- 

 tation stage, after which one half of the egg begins to divide 

 more rapidly than the other, and in this way a gastrula is 

 formed, by a process closely resembling epibole. The i\uthor, 

 from certain observations, was led to infer that in the present 

 species the formation of the gastrula commences at a later 



' "On Larval Forms of Bryozoa," ' Comptes llendus,' Sept. 6tli, 1875, 

 p. 443 ; 'Annals N. H.,' ser 4, vol. xvi, p. 301. 



