184 ALPHABETICAL COMPILATION 



HYBRIDS 



Hybrids of Arbacia Punctulata. — 



Arbacia punctulata ^ x Asterias forbesii 9- Few gastrulae, not maternal (Morgan, 



1893). Mathews, 1901c questions this hybridization. Tyler and Metz (1954) 



found that Arbacia eggs would not cross fertilize with Asterias sperm with or 



without trypsin treatment. 



Arbacia punctulata 9 X Echinarachnius parma ^. Plutei, maternal (E. B. Harvey, 



1942). Difficult cross (Just, 19 19, Matsui, 1924). 

 Arbacia punctulata ^ X Echinarachnius parma 9- Blastulae, maternal (E. B. Harvey, 

 1942). Plutei, not described (Just, 19 19). Plutei, maternal; cytology (Matsui, 

 1924). 

 Arbacia punctulata 9 X Lytechinus ( Toxopneustes ) variegatus ^. Few plutei, inter- 

 mediate; cytology (Tennent, 1912 b, c). Abnormal plutei (E. B. Harvey, 1942 

 unpub.). 

 Arbacia punctulata (J X Lytechinus (Toxopneustes) variegatus 9- Few plutei, inter- 

 mediate; cytology (Tennent, 1912 b, c). 

 Arbacia punctulata ^ X Mellita pentapor a (^.Flutei, more ina.termd {Tennent, 1910 b). 

 Arbacia punctulata 9 X Moira atropos ^. Plutei, more maternal; cytology (Tennent, 



1908, 1910b). 

 Arbacia punctulata ^ X Moira atropos 9- No data (Tennent, 1910b). 

 Arbacia punctulata 9 X Strongylocentrotus drobachiensis (^. Plutei, maternal (E. B. 

 Harvey, 1942). 

 Hybrids of Other Species. — 



Listed to 19 10 (Tennent, 1910 b, also in Morgan's Experimental Embryology, p. 

 613). See Tabulae Biologicae 1930, VI, p. 514 and "Other species", below. 

 Hybrid ( Heterospermic ) Merogones. — These are important in affording a means of 

 distinguishing nuclear and cytoplasmic inheritance. There are very few references 

 to hybrid merogones of Arbacia in comparison with those of other species. Chambers 

 and Ohshima (1922) were unsuccessful in fertilizing the non-nucleate fraction of 

 Arbacia eggs with Echinarachnius sperm, though with their own sperm (homospermic 

 merogones) they produced dwarf plutei with small nuclei. Fry (1927) obtained non- 

 nucleate fractions of Echinarachnius eggs fertilized with Arbacia sperm, but they 

 reached only the blastula stage. Attempts have been made to raise plutei by fer- 

 tilizing the non-nucleate halves o{ Arbacia, obtained by centrifuging, with the sperm 

 of Echinarachnius, but these have been abnormal and underdeveloped (E. B. H., 1941 

 unpub.). However, the non-nucleate halves of Sphaerechinus granularis obtained by 

 centrifuging, have been fertilized with Psammechinus microtuberculatus sperm in some 

 preliminary experiments done in collaboration with von Ubisch in 1934 and these 

 gave hybrid (intermediate) skeletons similar to the whole hybrids, thus showing 

 both nuclear and cytoplasmic influence. Further study of the skeleton of these 

 heterospermic merogones seemed desirable before publication. Von Ubisch has 

 recently (1954) published his results on these centrifuged merogones, also finding 

 the skeleton intermediate; he therefore infers that they are complete hybrids 

 and not merogones. In another series of experiments done in 1954 in which he ob- 

 tained non-nucleate merogones by cutting the Sphaerechinus egg, the skeleton was 

 paternal. 



The development of homospermic merogones of Arbacia obtained by cutting has been 

 studied by Tennent, Taylor, and Whitaker (1929) and by centrifuging by the author 

 (1932, 1940C, 1946c, and this Monograph, Part III). Some perfect but small plutei 

 have been raised from the fertilized red half-egg (See Plate X, Photograph 16). 

 Hybrids Occurring in Nature. — 



Echinus esculentus x E. acutus (Mortensen, Monograph, III, 3 : 36, 50, 136). 

 Echinus esculentus X E. elegans (Mortensen, Monograph, III 3 : 64). 

 Echinus esculentus x Psammechinus miliaris (Ibid., Ill 3 : 36), 



