MICROSCOPICAL STUDIES IN MARINE ZOOLOGY. 



BY JAMES HORNELL, 



Study XIV. — Spjlerozoum punctatum, a Colonial 



Eadiolarian. 



No group of animals possesses such intense interest to the 

 Biologist as does that of the Protozoa. Located on the very outskirts 

 of life, one searches among their lower forms and studies their every 

 phase and attribute, in the hope of obtaining the faintest clue as to 

 the origin of life itself. Their higher developments we scrutinize 

 equally closely, for evidence as to the particular evolution of the 

 sponges, simplest among the higher animals — those Metazoa whose 

 bodies are made up of aggregations of cells, not one of which is, of 

 itself, capable of prolonged separate existence, but requires the co- 

 operative assistance of other units, other cells, to carry on " life." 



The Protozoa are, we know, typically unicellular, but many of 

 the most interesting forms seem very closely to counterfeit the me- 

 tazoan plan ; though ever with this distinction, — separate one of their 

 cells, and straightway it can sustain long life and multiply its species 

 as though nothing radical had occurred. With these latter, our 

 attention now lies. 



Most of us have seen, and admired with enthusiasm, that lovely 

 emerald-jewelled rotating globe of colonial life, the tiny Yolvox of 

 our ponds. And though we cannot nowadays accept the firm belief 

 entertained by mariners of ancient times, that the sea contains coun- 

 terparts of everything moving on the land and in fresh water, yet as 

 regards Volvox, we may claim in Sphcero.zoum and its allies, at least 

 forms having many outward resemblances. 



Sphcerozoum is a colonial Eadiolarian in which the skeleton con- 

 sists of loose spicules surrounding each individual of the colony, but 

 before going into details of anatomy, it will be well for us to cast a 

 survey over the group wherein it is included. In the first place, 

 Radiolaria belong to that group of the Protozoa known as the Rhi- 

 zopoda, animals where locomotion and the capture of food is effected 

 by extensions (pseudopodia — " false-feet ") of the outer layer of the 

 body, ectosarc. The well-known Amoeba — long ago known as the 

 proteus animalcule on account of its constant change of shape, due to 

 the thrusting out of these pseudopodia first from one spot and then 

 from another — is one of the most primitive members. It is little else 

 than an animated microscopic speck of granular jelly-like protoplasm, 

 endosarc, surrounded by a slightly denser and clearer layer, the 

 ectosarc ; having a peculiarly- endowed dense S23eck, termed the 

 nucleus, embedded in the endosarc, and wherein lies the poten- 

 tiality for future multiplication. 



