PLATE XXVI 



Fig. i. A freshly caught specimen of Physalia, with the crest erect. 



Fig. 2. The saccus, removed from a living specimen, photographed 

 from beneath. 



Fig. 3. The same saccus as in fig. 2, but with a 50 g. weight resting 

 on it. 



Fig. 4. The endodermal muscle sheet of the saccus, showing cell out- 

 lines and muscle fibres (F. W.A., iron haematoxylin). 



Fig. 5. Detail of saccus muscle fibres, showing 'anastomoses' (F.W.A., 

 iron haematoxylin). 



Fig. 6. Another region of the muscle sheet, where some fibres have 

 buckled, revealing their double nature (F.W.A., iron haemat- 

 oxylin). 



Fig. 7. Contracted muscle fibres from the dorsal outpushings of the 

 saccus (Bouin, iron haematoxylin). 



