258 The Philippine Journal of Science 1913 



Vascular and nervous systems. — These two systems of organs 

 do not require description as they agree very closely with the 

 ordinary forms. 



Reproductive system. — In all the specimens which were dis- 

 sected, the nephridial sacs were full of spermatozoa or well- 

 developed eggs; also, in the stomata of the body wall numbers 

 of unripe eggs were often encountered, but although sections 

 were studied from almost every part of the body, including the 

 sheath of the nerve cord, the blood vessels, the body walls, and 

 the nephridial sacs, no traces of reproductive tissue of any kind 

 were discovered. Therefore, it seems probable that the forma- 

 tion of ova or spermatozoa must be limited to definite seasons. 

 From the finding of the partially developed eggs in the stomata, 

 it would seem probable that they are developed from the body 

 wall. 



A REVISION OF THE GENUS THALASSEMA 



Since the publication of Shipley's paper on the revision of the 

 Echiuroidea in 1899, in which there is given a key to the genus 

 Thalassema and a brief outline of the characters of the then 

 known species, there has been no attempt to revise the genus 

 as a whole. In the meantime, the number of known species 

 assigned to this genus has increased from 22 to 35. Also, a 

 number of the species mentioned by him have been obtained 

 in new localities, and in some cases important details have been 

 added to the descriptions. 



Shipley bases his classification, first, on the condition of the 

 longitudinal muscles of the dermal muscle layer and, secondly, on 

 the number of pairs of nephridia. In 1912, Spengel(43) provi- 

 sionally divides the group into 3 genera on the basis of the mi- 

 croscopic structure of the dermal muscle layer, without regard to 

 the number or arrangement of the nephridia. The characteris- 

 tics of these 3 genera have been stated already (page 252). In 

 regard to the first tw^o genera, Thalassema and Listriolohus, 

 the comparison of the muscle layers of T. sorhillans at different 

 stages (page 244) seems to indicate that these two are too 

 closely related to be separated into distinct genera ; the condition 

 found in the Listriolobus type — a thickening and thinning of 

 the muscular layer — seems to be brought about, from the form 

 in which the muscle is uniform in thickness, by a growth in 

 the regions of the bundles and a consequent pulling apart and 

 thinning of the interbundle region. In fact, in the 4 individuals 

 of T. sorhillans which were examined, all the stages from one 



