EARLY DEVELOPMENT OF GRANTIA COMPRESSA. 283 



amphiblastula larva is of gradual growth in the stages between the end of 

 cleavage and the final stages of the formation of the free-swimming larva. 

 I could not find any evidence for such segregation of materials as described 

 by Oonklin (1) in Cynthia, and I have come to the conclusion that, so far 

 as fixed material goes, no visible organ-forming areas can be demonstrated 

 in the egg of Grantia compressa. It is possible, however, that delicate easily 

 destroyed pigments may be present in the fresh ripe egg, and these might 

 mark out ground-protoplasmic areas not to be distinguished in fixed material. 

 Of this I have no evidence. 



(b) Chromidia and Mitochondria. 



Jorgensen and Dendy both describe the mitochondria under the name 

 " chromidia," implying that they have a true chromatinic nature and are 

 related to the nucleus. 



If the egg is treated by Champy-Kull's method the mitochondria are red 

 (fuchsin) and the nucleus is blnisn. In the Bensley-Cowdry stain the mito- 

 chondria are red (fuchsin) and the nucleus is green (methyl-green). In 

 Carnoy's fluid the mitochondria are dissolved away and the nucleus remains. 

 The mitochondria of Grantia are not " chromidia " in the proper sense of the 

 word, nor are they derived from the nucleus at any period of oogenesis *. All 

 embiyonic cells contain mitochondria, and there is no question of the latter 

 appearing from the nucleus at any stage of the oogenesis of egg-cells derived 

 from the amoeboid or other elements of the mesoglea or collar-epithelium. 



In a late paper on Apanteles I described true cytoplasmic chromidia in the 

 egg of this form ; such chromidia stain like chromatin, and ultimately r 

 metamorphose into secondary nuclei. In the Hymenopterous egg the 

 secondary nuclei (chromidia) and the mitochondria are easily distinguishable 

 and can be stained in different colours. 



(c) Fertilization. 



In this paper I have given the first correct interpretation of the peculiar 

 stages already described by Gorich, Jorgensen, and Dendy. It has been 

 demonstrated bey r ond a doubt that the spermatozoon of Grantia is brought to 

 the oocyte by a carrier-cell. On page 277 I have given my reasons for sup- 

 posing that the sperm-carrying cell is really a collar-cell which has lost its 

 collar and flagellum, and become amoeboid. 



Should subsecpaent work confirm this description (and 1 have little doubt 

 that there has been no mistake) this will constitute one of the most remark- 

 able occurrences in the fertilization of any animal. 



It is remarkable that the collar-cell temporarily containing the spermatozoon 

 should desert its position in the gastral epithelium and wander into the 



* I now abandon this view and admit Dendy's description of nucleolar extrusions to be 

 correct. This matter ia treated at length in my new paper in the Joura. Boy. Micr. Soc. 

 1920. 



