CCELENTERATA. 1 9 



just within the wall of the cyst, migrating later on to the centre. 

 Part of the protoplasm remains as a kind of network, and a 

 number of tubes (sporoducts) are formed, which are at first 

 directed inwards, but are later on turned inside out (everted), 

 projecting from the cyst, and serving as channels through which 

 the spores escape. This, of course, involves absorption of the 

 firm cyst at points where sporoducts are formed. From each 

 spore a single embryo escapes, which makes its way into one of 

 the epithelial cells lining the intestine of the cockroach. The 

 regions of the body are now gradually developed, the protomerite 

 and deutomerite projecting into the cavity of the intestine, while 

 the epimerite remains imbedded in the cell, and is soon thrown 

 off. The young Gregarina absorbs the digested food with which 

 it is surrounded, and quickly grows to the adult size. 



CHAPTER IL CCELENTERATA. 

 4. HYDRA (Fresh Water Polype). 



THIS is a small animal common in ponds, ditches, and stagnant 

 streams. Extended specimens measure from half an inch in 

 length downwards. There are two common kinds, the Brown 

 Hydra (Hydra fusca), and the rather smaller Green Hydra 

 (Hydra viridis). 



MORPHOLOGY. 



1. External Features (Fig. 4). The body of Hydra, when 

 extended (A), is in the form of a hollow cylinder, usually attached 

 to some object by its closed proximal end, which constitutes an 

 adhesive disc (the "foot"). The distal end is terminated by a con- 

 ical projection, the hypostome, in the centre of which is a rounded 

 opening, the mouth (m). Several (5 to 8) slender prolongations 

 of the body, known as tentacles (hi), project, at regular intervals, 

 from the base of the hypostome. Both body and tentacles may 



