I08 EDWARD POTTS : MICROHYDRA DURING I907. 



PLATE III. 



Consists of a series of Figures, i to 8, representing the gradual 

 development of a sexual medusa bud, observed by a party of five persons 

 during the night of May I7th-i8th, 1907, as sketched by them at the 

 hours marked. Attention is called to the pendant manubrium (m.) run- 

 ning through the whole series; — the somewhat diagrammatic radial 

 canals (r.c.) connecting with the marginal canals (m.c.),3 to 8, — and 

 particularly to the radial segmentation of the distal surface (d.) ; also 

 visible throughout the series from 3 to 8, and eventually forming the 

 "eight tentacles (t.) simultaneously," as a result of the throbbing pres- 

 sure against them of the velum (v.) connected with the marginal canal. 



PLATE IV. 



Figure i. Is a copy of the drawing made of the medusa (m.) seen 

 at about the same age attained by the last described, about ten years ago. 



Figure 2. Is a copy of the medusa bud (m.b.) at an early stage of 

 its development at the same date. 



Figure 3. Is a sketch of another Fresh Water Hydroid (h.), pro- 

 bably the fourth in order of discovery, found (three or four of them) 

 upon one of the stones from Flat Rock dam ; parasite upon a rhizome of 

 the polyzoan, Pottsiella (Paludicella) erecta, and strongly suggestive of 

 a marine form described by Sars (Rhizorgium roseum) , found on the 

 Baltic coast of Denmark. 



Figures 4 and 5. Progressive stages of the development of the 

 summer ovum of the same Pottsiella erecta, Kraepelin. 



