4 o 4 DISCOVERY REPORTS 



(3) The tentacles show an inherent rhythmic shortening and lengthening behaviour. The frequency 

 depends on the general degree of contraction within which the rhythmic movements take place, being 

 more rapid when the tentacle is contracted than when extended. Tentacles perform rhythmic behaviour 

 independently. 



(4) When extended, the larger tentacles of a medium-sized Physalia were estimated to measure 

 8-10 m. ; following stimulation they contracted within a minute to 12-15 cm. 



(5) The gastrozooids perform random, searching movements. The presence of food in the tentacles 

 does not appear to affect this behaviour. Gastrozooids respond to physical contact by spreading out 

 their buccal regions over the object encountered. 



(6) Strong stimulation applied to the float results in general contraction of all appendages. This 

 reaction is very rapid and, unlike the other reactions, appears to be through-conducted. 



B. Histology 



(1) Muscle is present in all four epithelia of the float but nerves are present only in the codon 

 ectoderm. 



(2) Polyploid cells, probably deriving from binucleate cells by combination of the two sets of 

 chromosomes during mitosis, are found throughout the float epithelia. Their distribution is 

 random. 



(3) The diploid chromosome number is 20, but mitotic aberrations are common and may lead to 

 the production of cells with abnormal chromosome complements. 



(4) Fragmentation of nuclei is demonstrable in the saccus-ectoderm and is attributable to the 

 excessive flattening and stretching of the layer. 



(5) Muscle-fibres are not visibly affected during mitosis in the nuclear layer. 



(6) The nerve-plexus has been demonstrated throughout the ectoderm except in the tentacles, 

 where technical difficulties have prevented effective study, and in the saccus where nerves are absent. 

 Nerves have not been located in the endoderm of any region. 



(7) The plexus is a diffuse one. Tripolar neurons predominate over bipolar. Many (possibly all) 

 nerve cells bear conical projections extending to the surface from which emerge two or more hairs, 

 presumed to be sensory. 



(8) Cellular processes or whole cells cross the mesogloea of Physalia from endoderm to ectoderm. 

 In certain regions they have short lateral diverticula. 



(9) The mesogloea has a laminated structure. Broad flat sheets cross one another. X-ray diffraction 

 tests point to the collagenous nature of the mesogloea. 



(10) A thin cuticle has been identified covering the ectoderm in many parts of Physalia. Evidence 

 is given for the secretion of this material from ectodermal gland-cells. 



(11) The chitosan test identifies the cuticular material as chitinous. X-ray diffraction tests agree 

 and, in addition, reveal the presence of a benzene soluble material, possibly lipid, in the cuticle 

 lining the air-sac. 



(12) In the ectoderm of the gas-gland three types of cell have been found. Results from an analysis 

 of the gaseous contents of the air-sac are given. 



(13) The large and small nematocysts occurring on the tentacles are holotrichous isorhizas. Small 

 isorhizas also occur in groups round the gastrozooid lip-region. Stenoteles occur in gastrozooids, 

 palpons and float. 



(14) Details are given concerning the fibrillar system found in cnidoblasts containing isorhizas. 



(15) Cnidoblasts with developing nematocysts are found in the tentacular ampullae, and over 

 other regions of the ectoderm. In the gastrozooids they tend to occur in small groups of even numbers, 



