120 Papers from the Marine Biological Laboratory at Tortugas. 



In 1909, at The Marine Laboratory of the Carnegie Institution at 

 Tortugas, the scope of the investigation was widened greatly by the 

 acquisition of new forms and the discovery that two of these forms 

 crossed reciprocally with equal facility. This, I believe, has given me 

 more favorable material than has been obtained by any other investi- 

 gator. The crosses made during this summer are shown in the following 

 list. The Hipponoe-Toxopneustes crosses are of especial interest. 



i 



Hipponoe esculenta 9 ( = Tripneustes esculentus) X Cidaris sp. &. 



2. Hipponoe esculenta 9 X Ophiocoma riisei d 1 . 



3 . Hipponoe esculenta 9 X Pentaceros reticulatus d 1 . 



4. Hipponoe esculenta 9 X Toxopneustes d 1 . 



5. Toxopneustes 9 X Echinaster sp. d. 



6. Toxopneustes 9 X Hipponoe d. 



7. Toxopneustes^ X Holothuria floridanatf. 



In 1910, at Tortugas, experiments with Hipponoe and Toxopneustes 

 were repeated and the observations of the previous summer were verified. 



This paper embodies that part of my work on cross-fertilization in 

 Echinoderms which pertains to the morphology of the embryos obtained, 

 and to methods of controlling the dominance of maternal and paternal 

 characters. 



Work on Echinoderm hybridization has been in the main of four 

 types: 



(1) Morphological studies, usually simple descriptions of larvae 

 obtained from various crosses. 



(2) Physiological sttidies, usually investigations of an analytical 

 nature based on observations of the effect of changes in environment 

 and made in the attempt to account for the resemblance of the offspring 

 to one or the other of the parents. 



(3) Cytological studies, researches carried on with the aim of cor- 

 relating microscopic characters of the hybrid material with those of 

 either or both of the parents. 



(4) Chemical studies, which have for their aim the solution of the 

 problem of fertilization in particular and in which the Echinoderm egg 

 is used incidentally because of its favorable nature. 



It will be a matter of some surprise, even to those familiar with 

 this work, to note the number and variety of the crosses which have 

 been made. In the list on the following page I have included all that 

 have come to my attention. 



It is an interesting fact that in most of these cross-fertilizations it is 

 the echinoid egg that has been fertilized by the sperm of other echinoids 

 and of asteroids, ophiuroids, crinoids, holothuroids and mollusks, while 

 reciprocal inter-class crosses have not been reported. This may or may 

 not be a matter of significance. In my own experience I have found 

 that the eggs of Pentaceros reticulatus are not readily fertilizable by the 

 sperm of Hipponoe, either after being allowed to stand or after treat- 

 ment with NaOH. In other experiments, in which I subjected the 

 Pentaceros eggs to treatment with CO 2 for from 4 to 10 minutes before 



