46 



LOWER INVERTEBRATES. 



myriads of green iRfusoria whose structure does not materially di£fer from that of 

 Epistylis, except the greater elongation of the canal-like extension of the contracticle 

 vesicle, which ascends to and surrounds the peristome. A notable structure is found 

 in the thread-like pedicles which unite the individuals of the whole colony. These 

 appear to be homologous with the branched stalk of Epistylis. In Ophrydium sessile 

 the pedicle is wanting, the bodies radiating from one point in the mucilaginous en- 

 velope. O. versatile and 0. eichornii are known to inhabit American waters. 



Stjb-Ordee IV. — Hypotricha. 



This sub-order includes numerous families and genera, nearly all of which are free- 

 swimming ; their bodies are smooth above, with variously disposed cilia below ; they 



are usually flattened and elon- 

 gate. Chilodon cucullulus af- 

 fords another stock form ; it is as 

 cosmopolitan as Paramecium 

 aurelia, inhabiting both salt and 

 fresh water. It has received 

 many names ; its flat, sub-ovate 

 body has the anterior apex turned 

 one side. The cilia on the ven- 

 tral surface are arranged in par- 

 allel lines. Its pharynx is sur- 

 rounded by a series of rod-like 

 teeth. Its food appears to be 

 diatoms, for these plants are 

 often found in its endoplasm. 

 Dysteria armata, described by 

 Huxley, is remarkable for the 

 indurated, complex pharynx. 

 The oral pit is strengthened by 

 a curved rod which terminates 

 in a bifid tooth. This is fol- 

 lowed by the pharyngeal appara- 

 tus proper, which may be said to 

 consist of two parts — an anterior 

 rounded mass in opposition with 

 a much elongated, styliform, pos- 

 terior portion. This part is quite 

 complicated, and cannot be clear- 

 ly defined in a few words. On 

 account of this complicated struc- 

 ture, and the single ventral stylet, 

 it has been considered a rotifer, 

 but recent research has brought to light facts suflScient to warrant the formation of a 

 family with this species as the type. A curious genus is Stichotricha, in which the ani- 

 malcules secrete a domicile ; several of the species live singly, but in one the stock is 

 branched, and a social group or colony is the result. This Kent has put in his new genus 



Fig. 46. — Schizosiplion socialis, eniaVged. 



