Studies of Jamaica Echini. 159 



proct, V is by far the more common, and in so far makes an approach to the 

 character of the Cidaridae where ocular V alone is frequently insert, but I 

 alone is rarely insert. In higher groups of the Centrechinoida, when one 

 ocular is insert, the order is more definitely fixed, as in the Arbaciid^e and 

 Echinometridae, where V is typically and I is rarely insert; or in the Echinid^ 

 and Strongylocentrotidae, where I is typically and V is rarely insert. Another 

 ocular peculiarity of Centrechinus is that where four plates reach the peri- 

 proct, I, V, IV, III insert is a rather frequent aberrant variant. This is a 

 very rare character in the higher Centrechinoida but is a common character 

 in the Cidaridae. 



Of the ocular characters of Toxopneustes variegatus, no special comment 

 is called for. It is simply the record from a definite locality, whereas my 

 previous record of the species was based on specimens from several locali- 

 ties. The peculiar zigzag pattern of color ornamentation shown recalls the 

 somewhat similar pattern seen in some of the Temnopleurida. 



In Tripneustes esculentus the ocular arrangement (figs. 10-17) is one of 

 the most interesting that has been found in any Echini. Two oculars 

 insert is commonly given as the species character, and it is the dominant 

 character in some localities (Bermuda, Florida). In Montego Bay this 

 character is acquired up to 90 per cent in specimens 40 to 50 mm. in diam- 

 eter, much less than half-grown. But in Montego Bay, as a local char- 

 acter, the species has gone much further and passed through a phase in which 

 oculars I, V, IV are insert like Bahama material, and finally takes on oculars 

 I, V, IV, II insert as the fully matured adult character. It is an exceptionally 

 interesting case as being the acquirement in late stages of growth as a typical 

 feature of a character which is a normal progressive variant of its own 

 species in other localities and also a typical advanced character in all 

 Echini which have four oculars insert. Looking at the test of a nearly grown 

 Tripneustes with its solid heavy plates, it is astonishing to realize that they 

 are still plastic and capable of allowing the readjustment of parts indicated 

 by the separation of genitals and traveling in of oculars so as to reach the 

 periproct. Not less surprising is the power of the law of ocular develop- 

 ment, that not any ocular, but a certain specific ocular, is the one that is 

 selected by the laws of growth to change its relative position. I know of no 

 more striking case of the definiteness of action in the growth of organisms. 



As stated, Echinometra lucunter is one of the very few species of Echini 

 characterized by having one ocular insert; therefore a series showing its 

 development is of interest. Four of the six species in the genus Echino- 

 metra are characterized by having all oculars exsert as the species feature, 

 and in these to have one ocular insert is a progressive variant. Also as a 

 family character, all exsert is the leading feature. Therefore for the genus 

 and for the family, Echinometra lucunter can be considered an advanced 

 type as regards ocular arrangement. In accordance with this fact it is not 

 strange, it might even be expected, that it would take on its advanced 

 character of oculars insert at a somewhat late stage as it does. The domi- 



