92 TH..'] ECHINODERMATA. §-§ 91, 92. 



sive power, united with tlie action of the cloaca, enables them to receive 

 into and expel from their interior the water of the sea/^^ 



The internal branchia3 of the Echiuridae consist of branchless tubes. In 

 Hchiurus vulgaris, the two branchiie, which are very movable and open 

 into a kind of cloaca, have, on their exterior, infundibuliform, ciliated pro- 

 tuberances ; and to each of these there is internally a corresponding cili- 

 ated sac, capable of being inverted. The very bright-red, vascular net- 

 work which is spread over these branchiae, communicates with the great 

 ventral vessel at the posterior extremity.'''' 



§ 91- 



II. Among the organs which are not exclusively respiratory, are the 

 ambulacra of the Echinodermata pedata, and the oral tentacles of the Ho- 

 lothurioidea and Sipunculidae, — organs Avhich are used also for prehension 

 and locomotion. 



These ambulacra and tentacles have always a cavity which communicate;? 

 directly with the proper vascular, aquiferous system. Their whole interior 

 is covered throughout with ciliated epithelium. 



This aquiferous system has, until recently, been taken by anatomists as 

 a special vascular one, or confounded with it. Its water serves partly to 

 distend the ambulacra and tentacles, as shown above (^ 77), and partly for 

 respiration, which is performed by the vesicles over which ramify the 

 branchial vessels. These vesicles are therefore like internal branchiae, 

 their vessels being bathed by the water of the sacs, and that of the cavity 

 of the body. Usually this system consists of a ring situated between 

 the vascular rays of the mouth, which sends canals to the oral tentacles 

 and to the sides of the body. These canals always pass along by the rows 

 of anibulacral vesicles, with which they communicate by lateral branches. 



§ 92. 



In the Echinodermata pedata, this aquiferous system has the following 

 modifications : 



In the Crinoi'dea, and Ophiuridae,*^' only traces of it have been found. 



In the first, there is an apparently aquiferous canal for the tentacles, 

 situated directly under their furrow. This may be regarded as forming a 

 j)art of such a system. In Pentacrinus, it is simple, but in Comatida, it is 

 divided at several points by simple septa.*-' 



In the Asteroidae, this system is highly developed, the central ring being 

 provided with pediculated and often elongated vesicles.'^' The main 



5 There is found, bat inconstantly, it would XXI. fig. 17) it wculd appear that Ophiurus has 



appear, upon the trunk of the branchiie of some an aquiferous system. 



)l')lothuriuae particular pedunculated coeca, which '^Müller, Abhandl. d. Berl. Akad. 1S41, p. 234. 



in Hohailschia rnarmorala have been regarded as 3 These ])yrlfi)rm vesicular appendages are al- 



urinary organs by Jaeger (Ue Holothuriis, &c., ways situated between the principal vessels of the 



I'ab. III. flg. 9, g.). But they require further rays, varying both as to number and volume, ami 



Livestlgation.* biding sometimes entirely wanting. Astropecten 



ö Forbes and Goodsir (Froriep''s neue Not. bispinosus has only five ; Asterisciis verrucii- 



No. 392, p. 277, fig. 12, e. — 19). latun, Astropecten pentncanthu.i, and Astera- 



l i'rom the figures of Delle Cliiaje (loc cit. Tav. canthion glacialis, have ten, in paii-s. In tliis 



•(§ 90, note 5.] For many new details upon 3/« «er. Arch. 1850, p. 129-155 (Si/napta, Chir- 

 the respiratory system of the Ilolothurioldea, see odota, and Molpadia). — Kd. 



