548 ' iJOBriNODERMATA. 
the circulatory system communicate inter se through the vascular ring 
encircling the oesophagus and reposing on the “ lantern ; the buccal 
feet communicate with the ambulacral vessels, the external branchiae 
only with the body cavity. There is no heart and no vascular net in the 
genital glands. The madreporite ” is chiefly an excretory apparatus, 
the presumed “ heart accolent to the sand-canal and abutting on the 
madreporite, a gland. The body-cavity is completely closed, and receives 
the sea water through absorption only Icf. Zool. Rec. xi. p. 611]. From 
these investigations, the author is inclined to doubt the truth of the in- 
terpretation given by Greeff and Hoffmann to certain features of the 
anatomy of the Asteridce, which he thinks it necessary to accept with 
reserve until ultimate conflfmation. Thus the anal vascular ring of the 
Asteridce and its branches communicating with the genital glands, cor- 
respond apparently entirely to the ano-genital ring and the excretory 
canals of the ovaries and spermaries of the Sea-Urchins, which have 
nothing to do with the vascular system, &c. 
It is impossible here to do justice to the profound comparative 
investigations illustrated by a long series of analyses of the utmost 
accuracy, of the structure, homologies, laws of composition and growth, 
of the shell of Sea-Urchins and its parts, which are laid down in 
Lov^)N*s “ ^Itudes ” (2). The flrst chapter is devoted to the peculiar 
organs (of taste ?) discovered by Lov^n, the Sphceridia (only wanting in 
• CiWans), their structure, arrangement, occurrence, &c. They are always 
placed on the ambulacra, in the peristomial portion, but very variable 
in number and position, according to genera and species, being sometimes 
inclosed or hidden in small cavities in the surface of the test, especially 
when the spines, tentacles, &c., cannot afford them a sufficient protection. 
The antero-posterior axis in the regular Echinidoe is determined by the 
position of the “ madreporite,” which is typically developed in the 
central plate of the apical system, this plate being however ordinarily 
connected with or altogether merged in the right anterior genital plate, 
which therefore is commonly designated as the “ madreporite,” and may 
serve as a means of orientation in the composition of the echinoid shell 
iJEchinometra is oblique, but Ileterocentrus and Oolobocentrus symmetrical). 
The modifications in the arrangement and development of the elements of 
the shell, successively introduced in the different genera of Echinida 
edentata, especially the Spatangidce, as they made their appearance in the 
course of time (e.g., the development of labrum and sternum), are 
traced in every detail, and worked out with sagacious penetration. In 
recent Spatangidce (with a single exception), the posterior genital plates 
are separated by the prolongation backwards of the “ madreporite,” as 
are also the posterior ocular plates ; in the older Spatangoid genera, the 
“ madreporite ” is separated from the impair inter-radium through the 
meeting in the median line of the genital and ocular plates. In S. 
adeta and prymnadeta^ the number of ambulacral plates in the ventral 
portion of the bivium is variable ; but in S. prymnadesmia (the predomi- 
nating recent type) the number is constant, the plates from the 6th to the 
8th or 12th of the inner series in the bivium being elongated transversely 
in a peculiar manner, towards the median line, and having their ambu- 
