ZOOLOaY AND BOTANY, MICROSCOPY, ETC. 347 



tissue of the nipple is next formed ; tlie teat may be developed early 

 (ruminants, horse, &c.), or at the end of foetal life (man). Next 

 secondary outgrowths arise from the primitive epidermal bud, as many 

 as there are ducts in the adults. At this period the differentiation 

 of the stroma from the mesoderm begins. Most of the primitive in- 

 growth disappears, a little remaining as the common orificial duct. 

 The secondary epithelial growths, on the other hand, grow farther, 

 become tubular, branch, and finally form the ducts (sinus and ducts 

 proper) and the acini. In the human foetus all the parts of glands 

 are developed by the time of birth. The development is according to 

 this same plan in all the animals investigated, comprising species of 

 Primates, Insectivora, Carnivora, Ungulata, Glires, and Didelphyda. 

 The so-called Montgomery glands are rudimentary milk-glands. The 

 view advanced by Creighton and Talma, that the acini are developed 

 from the mesoderm, is incorrect. The milk-glands cannot be regarded 

 as modified sebaceous glands, but are organs sui generis. 



Caudal End of Vertebrate Embryos.* — In his studies on the 

 development of Melopsittacus, Braun observed that a constriction is 

 formed around the end of the tail which leads to the construction of a 

 terminal knob, connected by a thin stalk with the base of the tail. 

 Into this nodulus caudalis the chorda and medullary tube originally 

 extend ; but they afterwards withdraw from it, leaving the nodulus, a 

 ball of mesoderm covered by epithelium, to be finally resorbed. This 

 discovery led Braun to search for similar structures in mammals, and 

 he now publishes his results. His investigations were made prin- 

 cipally on sheep embryos, and observations were also made on those 

 of other species. He finds an homologous structure, having, how- 

 ever, more usually a thread-like form. In sheep it may be readily 

 seen in most cases when the tail is from 1 • 5 to 3 mm. long. His 

 general results are : — 



1. The tail of mammalian embryos consists of two parts, an 

 anterior or basal vertebrate ; and a posterior invertebrate and smaller 

 portion, which, from its usual form, may be called the caudal thread. 

 2. The vertebrate portion may be partly or wholly imbedded in the 

 body (internal tail), and terminates at the sacral vertebrse in front ; 

 the division of the tail which protrudes is the external tail. 3. The 

 caudal thread contains originally the terminal portions of the chorda 

 dorsaliSj the medullary tube, and the caudal gut {Schwanzdarm), 

 These are the first parts of the thread to be resorbed ; the rest dis- 

 appears later, the epidermal covering lasting longest. 4. The caudal 

 gut is a rectal caecum ; before it is resolved it breaks up into single 

 parts, of which those in the tip of the tail endure the longest. 5. The 

 chorda dorsalis projects beyond the last vertebra, its ending being 

 often forked or contorted. 6. The medullary tube reaches to the tip 

 of the tail or the base of the caudal thread, and its posterior end is 

 probably resorbed. 



Braun further believes that he has found traces of a neurenteric 



• Arch. Anat. u. Physiol., Anat. Abth., 1882, p. 207. Cf. Science, i. (1883) 

 p. 261. 



