OutvER.— Marine Littoral Plant and Animal Communities. 507 
the integument assumes a tough, leathery texture, and allows a certain 
amount of drying without injury to the soft parts within. In such cases 
the mouth and gill-openings can be be closed by a sphincter. Members of 
the class Tunicata are commonly found a little distance above low-water 
mark. Those living under stones, such as Styela caerulea and Corella, have 
a rather soft test or tunic, colourless, white, pink, or bluish, and sometimes 
nearly transparent, so that the viscera can be distinctly seen through it. 
NN 
Fre. 1.—Part cross-section of thallus of Cystophora dumosa. 
Fic, 2.—Cross-section of thallus of Lessonia variegata. — 
Fic. 3.— Part cross-section of cortex of Durviilea antarctica. E 
Fic. 4.—Amphiroa corymbosa, an alga whose thallus is permeated with 
carbonate ot lime. à 
Frc. 5.—Half cross-section of thallus of Xiphophora chondrophylla. 
Fic. 6,—Half cross-section of thallus of Carpophyllum maschalocarpum. 
-Tunicata living on rocks between tide-marks, on the contrary, possess a 
tough cuticle, usually of a brownish colour (Polycarpa, Cynthia), but por 
i nia). The cuticle lies outside the ectoderm, and can stan 
It has been found in the British species 
e, a substance re ке» 
but rare i imals. One end of the test is fixed to the rock-surface ; the 
D s Са two apertures or siphons which can be opened and 
closed at the will of the animal. Sea-water passes ın through the oral siphon, 
]luses occurring between tide-marks are Onchidella 
а ge d The body is oval, with an arched back covered 
with a tough skin, somewhat slimy. These animal a 
of water without harm, though usually they seek shady crevices in the 
