62 bulletin: museum of comparative zoology. 



with the maturation stages, the best results were obtained by dissecting 

 out the ova, and then leaving them for a very short time in the higher 

 grades of alcohol, xylol, and paraffine. Four minutes in each of the 

 former, and three in tlie paraffine, melting at 50° Centigrade, secured a 

 good penetration, but did not entirely prevent crumbling. Painting 

 the sections with flexible collodion was resorted to, but while this held 

 together the section that was being cut, it also pulled part of the yolk 

 out of the next section, and imperfect series resulted. Double imbed- 

 ding with celloidin and paraffine was also tried, but this made the yolk 

 too brittle, so that I am still in quest of a satisfactory method for this 

 material. 



The sections were cut 6 fx thick, and fastened to the slide with tap 

 water, which was evaporated at about 36° after the sections had been 

 stretched by subjection to a slightly higher temperature. This method 

 gave perfectly satisfactory results, and possesses the immense advantage 

 of leaving no foreign substance on the slide. 



I wish to express here my thanks to Dr. E. L. Mark, under whose 

 direction this research has been carried on, and to whose constant kind- 

 ness the credit of much that may be of value therein is due. 



II. Sexual Organs. 



1. Development in Distaplia occidentalis. 



Old colonies which had already reached sexual maturity are the 

 only ones in which I have studied the development of the sexual or- 

 gans. In such colonies, all of the buds, even the smallest and least 

 differentiated, possess the fundament of the ovotestis. Figure 1 (Plate 1) 

 represents a section through such a bud. The large germ-cells, which 

 indicate the presence of the ovotestis, are situated entirely on one 

 side of the flattened inner vesicle, and all of the evidence indicates 

 that this side is dorsal ; for, as soon as the axes of the bud are estab- 

 lished by the development of the other organs, the ovotestis is found to 

 lie in the mid-dorsal line. The rather indiscriminate mingling of the 

 young oogonia and primordial follicle cells, and the superficial ^ position 

 of the oogonia as contrasted with the deeper position of the less differ- 



^ Following Jiilin ('03, p. 95), I use the terms superficial and deep as relating to 

 the position of the structure in question with reference to the whole individual. 

 Peripheral and central are used onlj to describe position with reference to the organ 

 itself. 



