524 ti. H. Newman 



were as follows: 118, 112, 112, 104, no, no, 120, no, 114, 98. 

 Average 110.8. A few poorly developed specimens were noticed, 

 resembling the condition of M hybrids at 80 hours {m6). About 

 90 per cent, however, were large and healthy looking. 



The M pures were about the size of the best of the M hybrids. 

 About 10 per cent, however, had died since the last examination. 

 There were several ill-developed and anaemic specimens. The 

 heart rates often specimens were as follows: 82, 80, 78, 78, 80, 82, 

 80, 80, 82, 82. Average 80.4. Although there was a complete 

 vitelline circulation there was no pigment on any of the specimens. 

 The heart-beat in the M pures was nearly two days later in appear- 

 ing than in the H pures. The pigmentation was still more mark- 

 edly slower in making its appearance (Plate IV, M8). 



Stage 9 (168 hours or 7 days): Several stages were examined 

 • between the last stage described and the present one, but there 

 was no very noteworthy change in the relative conditions of the 

 four strains. At this period the H pure embryos had grown con- 

 siderably in size, the eyes had reached almost their definitive form 

 and were darkly pigmented. The pigmented areas were well 

 marked and consisted of large chromatophores. The pectoral 

 fins had appeared and were in a continual state of vibration, prob- 

 ably performing a respiratory function. The heart-beats were 

 difficult to count on account of the opacity of the body, but from 

 special studies on other series it appears that the rhythm estab- 

 lished at Stage 8 is maintained at least up to hatching. The 

 capillaries and vitelline vessels were covered with brownish black 

 pigment. Larger chromatophores of a lighter brown color were 

 found between the capillaries. 



The H hybrids (Plate IV, hg) were on the average equal in size to 

 the ijT pures (Plate IV, i^p),but ag a rule were much less heavily 

 pigmented, many being decidedly pale. About 10 per cent of the 

 hybrid embryos were, however, at least as heavily pigmented 

 as any of the H pures, and some of these dark hybrids were notice- 

 ably larger than the largest of the H pures. The poorly developed 

 specimens showed all degrees of advancement. Some of them 

 lacked a circulation, although the heart was present and was beat- 

 ing at a fairly high rate. The hearts of some were shrunken 



