ZOOLOaY AND BOTANY, MICROSCOPY, ETC. 331 



Morphology of the Amphineura.* — Dr. A. A. W. Hubrecht gives 

 a convenient summary of the actual state of our knowledge of this 

 class of animals, including a brief statement of what is " known, 

 surmised, uncertain, or unknown," with respect to (a) integument, 

 (&) nervous system, (c) intestine, (d) circulatory and respiratory 

 apparatus, (e) reproductive and excretory organs. 



Molluscoida. 



New Synascidian.l — Dr. E. Drasche describes Oxycorynia fasci- 

 cularis, which are found in cylindrical trunks of as much as 6 cm. 

 in length ; the colour of the colony is a dirty green, and the in- 

 dividuals which are only 10 mm. long have the branchial sac 6 mm. 

 long. The rounded cloacal orifice is found at the uppermost tip of 

 the sac. The animals are connected together by a very delicate and 

 transparent tunic. The nearest ally would seem to be the Chon- 

 drostachthys of Macdonald. 



Alternation of Generations in Doliolum.^ — Dr. Carl Grobben 

 describes this phenomenon in detail, and amongst more general 

 considerations, points out that nearly all animals which reproduce 

 themselves by gemmation are of a fixed habit, the matter which is 

 not used up in the work of locomotion being applied to the pro- 

 duction and nutrition of buds ; gemmation being inconveniently 

 carried on by a free-swimming form, we must suppose that such free 

 forms as do multiply thus are derived from ancestors that were fixed ; 

 we have a good example in the Siphonophora, and the same view 

 may be applied to the SalpidsB. 



The simplest mode of alternation of generations is, perhaps, to 

 be seen in some compound Ascidians, where the individuals that 

 arise from ova are sterile, while those that are developed from buds 

 develope generative organs. This is a division of labour. In 

 Pyrosoma the ovum gives rise to a cyathozooid, whence appear 

 four ascidiozooids, and these multiply either by gemmation or by 

 the formation of sexual elements. In the true Salpidte the nurse 

 developed from the egg gives rise to a chain of apparently very 

 different forms which are altogether sexual in their mode of develop- 

 ment. Here then there is a complete division of labour, and this is 

 clearly due to their free life. Coming lastly to Doliolum, we find 

 that here the larva developed from the egg, after losing its tail, 

 gives rise to lateral and then to median buds, which latter provide 

 the sexual forms. The differences between the zooids are consider- 

 able : the nurse has nine, the sexual form has only eight muscular 

 bands ; the former has an auditory organ which the latter is with- 

 out ; the first nurse of Doliolum has its stolon dorsal, and is there- 

 fore without a homologue in the rest of the Tunicata ; in other words, 

 it is a structure which has been independently developed, and in 



* Quart. Journ. Micr. Sci., xxii. (1882) pp. 212-28 (11 figs.). 



t Zonl. Anzeig., v. (1882) pp. 162-.3. 



X Claua' Arbeit., iv. (1882) pp. 201-99 (5 pl.s.). 



z 2 



