274 Resting Eggs, or Statoblasts of a Plwmatella. 



imitated than in my jar and bottle, the fate of the statoblasts 

 might have been different. More might have developed, and 

 those that emerged from their curious resting-house might have 

 lived the full term of their race, and resembled the fruitful vine 

 in the number of branches they would have put forth. 



As some readers may not be familiar with the charac- 

 teristics of the polyzoa, a few words on that subject may 

 not be out of place. In form they resemble the compound 

 polyps, with which group they were formerly confounded, but 

 their structure is more complex, and their zoological rank 

 higher. The polyps have no distinct membranous stomach, 

 but only a cavity with one orifice; they are, in fact, living 

 bags, having, as Dr. Grant says, " a variable number of highly 

 prehensile tubular tentacula round the mouth." The polyps 

 belong to the sub-kingdom Cselenterata, defined by Professor 

 Greene in his excellent Manual* as " animals whose alimen- 

 tary canal freely communicates with the somatic cavity" {i. e. 

 general cavity of the body) . Substance of the body made up 

 of two foundation membranes, an outer or extoderm, and an 

 inner or endoderm, which correspond in mode of growth with 

 the primitive layers of the germ; no distinct neural and 

 hasnial regions, and nervous system absent in most. Peculiar 

 urticatory organs or thread cells usually present." The polyzoa 

 have a distinct digestive tube with two orifices, one for entrance, 

 and the other for exit. Their tentacles are stifferin appearance, 

 and not warty looking, as in the polyps, and they are furnished 

 with two rows of cilia, the motion of which is always up one 

 side and down the other. The intestine is bent round, so that 

 the anus lies near the mouth, and one nervous ganglion situated 

 near the mouth is ver}?" easily seen in many species. This 

 ganglion acts as a rudimentary brain, and seems the source of 

 the nerve power belonging to each individual. Eecently 

 Dr. Fitz-Miiller has discovered that these creatures also possess 

 what he terms a " colonial nervous system," f which establishes 

 a communication between each individual and the colony of 

 which he forms a part. 



To return to my statoblasts : I may mention that I am still 

 keeping them to see whether any further histances of develop- 

 ment will occur, and I should recommend any one who pos- 

 sesses a fresh-water aquarium to endeavour to raise colonies of 

 these very beautiful and highly interesting animals by similar 

 means. 



* Manual of the Sub-7cingdom Ccelenteraia, by Joseph Keay Greene, B.A., 

 Professor of Natural History, Queen's College, Cork. Longman, 

 t See Intellectual Obseeveb, No. vii. p. 67, vol. ii. 



