224 HARGITT. [VOL. II. 



years devoted to the embryology of the species common in the 

 waters of the Massachusetts coast,-- P. Tiarella McCr. A criti- 

 cal study of these medusae is, however, rendered difficult and 

 tedious owing to their minuteness and form. In size they 

 are only about .8 mm. in diameter by about 1.5 mm. in length. 

 The highly oval form renders difficult a study of the aboral 

 surface and the junction of the radial, or chymiferous canals, 

 -a point of considerable variability in many cases in other 

 genera, notably Gonionetnus, to be noted later. In a study of 

 their morphology Smallwood ('99) has pointed out the variability 

 in the structure and development of these canals. He has 

 shown that in a considerable proportion of specimens there is 

 a tendency to atrophy both in the radial and circumferential 

 canals, especially the latter. These changes are not evident 

 in a surface study of specimens, the pigmentation which marks 

 their course being fairly constant. The principal variation to 

 which I desire to direct attention in this connection is a physi- 

 ological one, viz., a rather marked variation in habit and activity. 

 I have discussed elsewhere this feature ('00) and need only refer 

 here in brief to those observations. As there pointed out, there 

 seem to be two rather distinct features of habit ; namely, a 

 rather deep-water habit upon rocks, seaweed, piles, etc., and a 

 surface habit upon eel-grass or similar support, which serves to 

 bring the colonies to the surface, thus often in a low tide 

 exposing them directly to the action of the midsummer sun 

 and temperature. 



Associated with these differences are correlated variations 

 in the form and color of the colonies, or, as Bateson would 

 designate them, " substantive variation." The surface or eel- 

 grass varieties exhibit more distinctly the pinnatifid character 

 which marks its specific peculiarity, due doubtless, in part at 

 least, to the prone or floating disposition of the colonies. 

 Associated also with this is the much higher coloration so con- 

 spicuous in these specimens, a variation extending not only to 

 the perisarc of the colonies but also to the medusae and the 

 eggs, which are rather bright orange, while those taken from 

 the deeper waters are a pale, creamy white, with the slightest 

 trace of pink in many cases. 



