124 ZOOPHYTES. 



I have also seen several of the first Medusse, both before and after libera- 

 tion, and all alike free. ' 



To these and other points I shall venture to direct the general atten- 

 tion of naturalists. Scotish observers will find the proper season of their 

 enquiries regarding the hydra indefinite, but regarding the Medusae they 

 are restricted from about the first of February until the first of May. No 

 Medusse were produced from the hydrse in my possession, after the 15th 

 of April in the year 1846. 



But the subjects are so diminutive and so perishable ; of such rare 

 and uncertain occurrence, as to preclude any premeditated course of obser- 

 vations ; or the expectation that a series interrupted may be resumed and 

 completed fi-om new specimens, at any given time. Hence a perfect his- 

 tory of them would require the united labour of many observers for many 

 seasons, aided even by fortuitous and advantageous incidents. 



Little remains for addition to this already too prolix detail. It has 

 become so from an anxiety to render an obscure and difl5cult subject in- 

 telligible by those who may not have the benefit of practical experience. 



All the Medusse in the embryonic roll are separate and distinct ani- 

 mals. Each is in close application to that which is next below, if itself 

 be uppermost ; or lays between two if intermediate. The proboscis is 

 outermost if the individual be uppermost in the roll ; thus all lie in the 

 same direction, the proboscis outermost, as the Medusa escapes, from the 

 next left behind. When the last remains in adhesion to the fleshy bulb, 

 its proboscis projects outwards also. Thus the under surface of the em- 

 bryo is always outwards, while a portion of the roll. 



This is a singular arrangement : it shews that Nature designs that the 

 maturity of the embryos, and their liberation into active life, should be 

 successive. Whether the brood be confined within some invisible amnios, 

 collectively or individually, in an earlier or later stage, is uncertain. 



The period occupied by the change, and that which is consumed in 

 the dissolution of an entire roll, is extremely variable. It usually takes 

 several days. But I have seen a single Medusa free itself within three 

 minutes after its precursor departed. The higher two of Plate XX. 

 fig. 16, separated during observation. The four higher of Plate XIX. 



