136 



FIELD. 



[Vol. XI. 



Ophiuroidea. 



this smallness is in certain cases of great advantage to the in- 

 vestigator it has up to the present time prevented a comparative 

 study of the spermatogenesis of the echinoderm groups. By 

 the use of remarkably good apochromatic objectives (3 mm.: 

 apert. 1.30 Zeiss) and compensating oculars, I have been able 

 to study the process in several representatives of each class. 

 The species studied included : 



Stichopxis regalis. (Salenka.) ^ 



Holothuria Poli. (D. Ch.) iHolothurioidea. 



Cucumaria ciicumis. (C Planci.') J 



Antedon rosacea. (Norman.) } Crinoidea. 



Echinus microtuberculatiis. (Blr.) 



Sphaerechiims gramilaris. (Ag.) 



Strongylocentrotiis lividiis. (Brandt.) J>Echinoidea. 



Arbacia ptistulosa. (Gray.) 



Ec/ihtocarditwi cordatw/i. (Gray.) 



Ophioglypha lacetosa. (Lyman.) 



OphioDiyxa pentagona. (Miill., Fr.) 



Ophiothrix fragilis. (Miill.) 



Ophiodei'ma longicatida. 



Chaetaster longipes. (Miill., Fr.) 



Astropecten pentacatithus. 



Asterias glacialis. (O. F. M.) 



Echinasier sepositus. 



Asterias Fo7'besii. 



Many other species were examined. Those species which 

 show any marked deviation from the typical dioecious condition 

 as do, for example, the hermaphroditic forms such as Synapta, 

 Asteriua, etc., or those which have become viviparous as, e.g., 

 AmpJiiura sqiiamata, have been intentionally avoided. The 

 other species examined were either obtainable only in limited 

 numbers, or at the time the sexual organs were in an unfavor- 

 able condition. 



As was to be expected, throughout the phylum the general 

 aspects of the process were found to be closely similar. 



In case of several species of Echinoidea which were examined 

 the reproductive organs were found to be infested by a sort of 

 "yellow cells," apparently an alga (see PI. XVI), Fig. 13. So 

 far as I am aware, these have not been described. They were 

 found frequently in Arbacia pustulosa, but most abundantly in 



Asteroidea. 



