90 MICROSCOPICAL STUDIES. 



crawl about like so many miniature Octopods. This free life is rapidly 

 run and then they settle down and become attached to rock or weed. 

 In this situation they rapidly reproduce, by continued budding, the 

 typical hydroid stock. Here, then, there is no trace whatever of 

 medusae, whether fully developed as free-swimming organisms, or 

 bereft of a free existence and tied for life to the mother polypite : 

 nought is left of the medusa-stage save the reproductive organs, 

 and as these are, among the Gymnoblastic Hydroids, situated in the 

 walls of the manubrium, we may homologize the sexual buds of 

 Coryne, with the manubria of such medusa?. 



As Obelia may be taken as typical in every sense of the 

 Calyptoblastic Hydroidea, where the polypites are lodged in 

 cup-like expansions of the horny perisarc, the medusa? usually 

 provided with otocysts (rarely with eye-spots), and the genital 

 glands developed upon the radial canals, so Coryne and Syncoryne 

 may be taken as the types of that other great division of the 

 Hydroidea, known as the Gymnoblastic characterised by the 

 polypites being naked or athecate, the medusae, when produced, 

 provided with eye-spots (ocelli) and never with otocysts, and 

 with the genital glands lodged in the walls of the manubrium, and 

 not in the course of the radial canals. 



To the student of the smaller forms of marine life, the stems 

 of the Corynidae offer endless material for research, so abundantly 

 are they clothed, at times, with a fluffy growth that under the 

 microscope is revealed to consist of multiform Diatoms, lovely in the 

 delicacy of their glassy sculpturing and in the rich hues of the living 

 matter within them ; of more minute Infusorians, the cups, and bells 

 and tassels of those that live their lives attached, and still smaller 

 forms, cilia-rowed and free-swimming, that speed and rotate and take 

 eccentric course among the miniature undergrowth upon the crowded 

 stems ; here and there too, can be spied a slow-crawling Foraminifer 

 whose porcellain-white shell gleams brilliantly, while from innu- 

 merable pores stretch living threads along which hurry, this way 

 and that, the tiny particles that are engaged in the life-building 

 of the tiny creature ; the stout bobbing heads of that curious Polyzoon, 

 Pedicellina, are frequent, curtseying and bowing to one another, 

 with old world homage ; to the keen-eyed, interesting forms of 

 Rotifers, so rare in the sea, may occasionally reveal themselves spin- 

 ning erratic course through the water or climbing about with jerk 

 and double among the rich growth of the tiny algae that form never- 

 theless the giants of this tiny microscopic forest. 



None of these can be accounted parasites ; they occasion no 

 harm to the host and simply live together a crowd of commensals. 



