DEPARTMENT OF MARINE BIOLOGY- II3 



sp., Stichopus mcchii, Echinaster crassispma, and Holothuria mexicana. In 

 all of these forms the gonads appeared in very immature state, with the 

 exception of Holothuria mexicana. Dr. Mayer kindly offered to preserve 

 eggs of the latter in maturation phases, but reports that when he left the Keys, 

 in the latter part of July, the eggs were still unripe. Only a single specimen 

 of Bchinastcr was found at Tortugas, but sections of the ovary show that 

 this is a highly promising form for future study. I have since learned that 

 this echinoderm is very abundant at the Marquesas Keys, and I hope to be 

 able to procure material during another summer. 



The eggs of Holothuria mexicana appear very peculiarly favorable for pur- 

 poses of the present investigation, and it is a source of deep regret to me that 

 I could not procure ripe material before the laboratory closed for the season. 

 Attempts were made to force the eggs to mature by artificial means, such as 

 warming the water, agitation, acid solutions, and the addition to the sea- 

 water of the active spermatozoa of Hipponoe, but to no avail. The &gg of 

 Holothuria mexicana has a large micropyle; the spermatozoa of Hipponoe 

 esculenta are small and very active; theoretically it should be possible to 

 make a very pretty and highly interesting cross between the two. Various 

 ophiurans to all appearances offer equally favorable spermatozoa for such a 

 cross. The great abundance of echinoderms furnishes material for the solu- 

 tion of many problems to one fortunate enough to be in the waters of Tor- 

 tugas during the proper seasons. One is strongly impressed with the fact 

 that in the tropics the breeding seasons of the animals are just as definite and 

 as sharply limited in time as in the temperate zones. 



The egg of Hipponoe esculenta has tv/o or more nucleoli, thus contrasting 

 sharply with Asterias forbesii, which has constantly only one. Furthermore, 

 the egg matures in the ovary, and this fact renders it less favorable for a 

 study of maturation phenomena than the egg of Asterias, which matures after 

 being shed into sea-water. However, sections of ovarian material gave 

 sufficient of the maturation phases for the study contemplated. Attempts 

 w^ere made to cause immature eggs to mature in sea-water under stimulus of 

 agitation, acids, etc., but without success. But unfertilized mature eggs 

 could be induced to undergo the first two segmentation divisions under the 

 stimulus of a drop of HCl added to the sea-water. Controls showed the com- 

 plete absence of spermatozoa from the water. 



In Hipponoe two polar bodies are formed, the first never being seen to 

 divide. The reduced number of chromosomes is approximately 18 and 

 maturation appears to take place by a double longitudinal division. Con- 

 cerning the earlier stages of the maturation process, more definite statements 

 can be made. The chromosomes arise from the nuclear reticulum, which 

 assumes the form of a loose spireme and increases in chromatic content prob- 

 ably at the expense of the vanishing nucleoli. The stout spireme contracts 

 into a closely tangled knot and then segments into the reduced number of 

 chromosomes, which are presently drawn into the first polar spindle. Thus 

 the chromosomes, in contrast to what occurs in Asterias, where they are 

 formed at the beginning of the growth period and persist with identity 

 unimpaired, are merged with the nuclear reticulum and only arise as recog- 

 nizable chromosomes at the very close of the growth period. ' Similarly, then, 

 as in Asterias, the chromosomes originate from the nuclear reticulum and 

 receive chromatic material, probably a nutritive substance, from the disap- 

 pearing nucleoli just prior to their entrance into the first polar spindle. 



