MARINE BIOLOGICAL STATION AT PORT ERIN. 103 



tection against injury, and this loss is compensated by the 

 colours and appearance of the soft bodies, which in some 

 cases are of a protecting and in other cases of a warning 

 nature. The spawn of the sea-slugs is deposited in long 

 ribbon-like or cord-like convoluted white masses on stones 

 and weeds. A small piece contains many hundreds of 

 minute embryos which, when hatched, have for a time 

 little cap-like shells. This leads us to believe that the 

 sea-slugs are descended from ordinaiy shell-bearing 

 Molluscs. 



Papers and reports upon our Nudibranchs, by 

 Professor Herdman and Mr. Clubb, will be found in our 

 volumes. 



TUNICATA. 



(Fig. XXI.) 



The Ascidians, or sea-squirts, are not so well known 

 to the public as they deserve to be. They are very 

 common, very varied and some of them very beautiful. 

 Most of them when adult stick to stones or sea-weeds, and 

 they are of two kinds — the Simple Ascidians and the 

 Compound Ascidians. A Simple Ascidian, such as Ascidia 

 (fig. XXI. 1), is a grey sack-like body from 1 to 6 inches 

 in length, having a tough skin (the " Tunic," hence 

 Tunicata) and 2 openings through one of which the sea- 

 water is drawn in, while it is squirted out through the 

 other. When touched incautiously, the animal contracts 

 and emits sudden jets of sea-water from both apertures, 

 thus vindicating its title to the popular name " sea-squirt." 

 The name Ascidian (from the Greek " Ascos," a leathern 

 double-necked bottle) is given in reference to the bag-like 



