62 MICROSCOPICAL STUDIES. 



a thinning takes place at the apex, and finally gives way 

 to permit of the extrusion of the polypite's tentacles) ; 

 g, gonotheca ; m, medusid buds in different stages, within 

 the gonotheca. 



Fig. 3. View from below of a freed medusa. 

 Fig. 4. Diagram of same, 



Fig. 5. Diagrammatic vertical section through same. The section 

 follows the course of a radial canal on the right side, 

 while on the left, an interradial portion of the disc is 

 sectioned. 



Fig. 6. A Medusa, considerably older than that shown at Fig. 3, 

 seen reverted and from the side. It had just captured 

 an Arrow-worm (Sagitta), which is doubled up, the bend 

 being within the digestive cavity of the Medusa. 

 Lettering the same for Figs. 3 6, viz : a, atrium ; c.c, circum- 

 ferential canal ; en, endoderm ; g.g, genital glands ; m, manubrium ; 

 o, mouth ; ot, otocyst ; r.c, radial canal ; s.u, sub-umbrella ; t, ten- 

 tacle ; u, umbrella ; v. velum. 



STUDY XII. ON POLYNOE PROPINQUA AS TYPICAL OF THE 

 HIGHER ANNELIDS. 



Polynoe propinqua (Malmgren) is an elegant marine annelid, 

 short and slender in its proportions, rapid and lively in its movements. 

 When the tide recedes, its haunts are to be found wherever boulders 

 litter the shore, and many a weary backache have I had through a 

 course of such stone-turning. It is easily recognized by reason of 

 two rows of oval overlapping brownish scales that lie upon its back, 

 and from under which project, oar-like, on either side, serried banks 

 of lovely translucent paddling-bristles. A pretty creature, but loath 

 to be captured. Alarmed at the approach of the forceps, it squirms 

 and makes desperate effort to escape, and indeed if it be lifted 

 roughly and by force, instead of being taken by some gentle snare, 

 lo ! it breaks into pieces and is to you but a worthless capture. 



A cursory examination suffices to show that except for the two 

 extremities, the body is divisible into about 41 ring-like portions, all 

 broadly or obviously of the same value one with the other formed 

 fundamentally upon the same plan, though some are either internally 

 or externally modified in particulars for special functions. The 

 typical form of these equivalent body-rings, or somites as they are 

 termed, possesses on either side a fleshy two-branched lobe, the 

 parapodium, in which are implanted bundles of finely sculptured 

 bristles or setae. The upper branch, the notopodiuin, is considerably 



